The mechanical analysis model of 3D four-directional braided composite under complex loadings were developed based on the helix geometry model and finite multiphase element method. The failure points of 3D four-directional braided composites under tension-tension and tension-shear loadings were predicted when different loading ratios are imposed upon the unit cell，and failure envelopes were obtained. The results show that the braiding angle has a significant effect on the mechanical properties of 3D braided composites under complex loadings. The impact of loading ratios on the failure of braided composites should receive more attention. The present numerical method provides an effective tool to predict the mechanical properties of 3D braided composites under complex loadings.