This paper aims to address the challenges faced by traditional airborne electro-optical pods in high-precision target detection and recognition in complex environments. These challenges include limited field of view， energy loss due to central obscuration， insufficient spectral coverage， and small zoom ratios. To overcome these limitations， a multispectral off-axis common-aperture continuous zoom optical system is designed. The focus of the study is on constructing an optical architecture that balances large aperture size， wide spectral coverage， a large zoom ratio， compactness， and engineering feasibility. The system is designed to achieve high-quality continuous zoom imaging under unified aperture conditions in the near-infrared， short-wave infrared， and mid-wave infrared spectral bands.The overall system adopts a combination of a "front off-axis afocal telescope system + rear entrance-pupil-forward continuous zoom system." The front common-aperture section employs an off-axis reflective structure， where the initial configuration is based on a coaxial three-mirror structure. Through eccentric， tilting， and folding adjustments， the system is shifted off-axis to eliminate central obscuration while reducing the system's axial dimension. The rear continuous zoom section addresses the challenges of balancing long and short focal length aberrations in traditional entrance-pupil-forward zoom systems by introducing a field lens before the zoom system. This setup allows collimated light from infinite distance to be projected onto a fixed intermediate image plane， ensuring image plane stability during the zoom process. The system design optimizes pupil matching and minimizes aberrations across different spectral bands. Specific designs are created for the near-infrared， short-wave infrared， and mid-wave infrared channels， where the mid-wave infrared channel incorporates YNI value control and cold stop matching to reduce stray light from cold reflections. Two beam-splitters are introduced in the parallel light segment of the front telescope to separate the three spectral bands and achieve a compact system layout. Comprehensive evaluations are carried out， including modulation transfer function analysis， field curvature， distortion， tolerance Monte Carlo simulations， and zoom curve analysis.The proposed multispectral off-axis common-aperture continuous zoom system features an optical aperture of 200 millimeters， a maximum linear field of view of ±6.15 millimeters， and a maximum zoom ratio of 6×. The near-infrared channel covers a continuous zoom range from 200 millimeters to 1200 millimeters， the short-wave infrared channel spans from 300 millimeters to 1200 millimeters， and the mid-wave infrared channel operates from 200 millimeters to 800 millimeters. The front off-axis telescope system has a total axial length of only 430 millimeters， with wavefront aberrations smaller than 0.05λ across both large and small field-of-view conditions， ensuring high-quality imaging at the front end. The system's performance across the three spectral bands is excellent. The modulation transfer function in the near-infrared channel is greater than 0.3 at 110 line pairs per millimeter， in the short-wave infrared channel， it exceeds 0.4 at 33 line pairs per millimeter， and in the mid-wave infrared channel， it remains above 0.2 at 33 line pairs per millimeter， demonstrating strong imaging contrast across all focal lengths. Field curvature and distortion analyses indicate that the system has excellent field curvature correction， with slight distortion at short focal lengths， but the distortion remains within acceptable limits for all focal lengths. A Monte Carlo tolerance analysis， performed with 1000 iterations， reveals that the system maintains diffraction-limited modulation transfer function at the Nyquist frequency with an 80% probability for both long and short focal lengths， even when accounting for manufacturing and assembly errors. The zoom curves for all channels are smooth， showing no abrupt changes， which facilitates the design of the zoom mechanism and ensures stability in the zoom process.The proposed multispectral off-axis common-aperture continuous zoom optical system successfully addresses the challenges of traditional optical designs， including central obscuration， limited field of view， and small zoom ratios， by offering a high-quality solution with a large zoom ratio and wide spectral coverage. The system delivers excellent continuous zoom imaging performance across the near-infrared， short-wave infrared， and mid-wave infrared spectral bands while maintaining stable optical performance over the entire zoom range. The off-axis reflective structure and improved entrance-pupil-forward continuous zoom system design ensure compactness and efficient energy utilization， making the system suitable for practical engineering applications in airborne multispectral electro-optical pods. This approach represents a significant step forward in the design of optical systems for target detection and recognition in complex environments.