A modeling and optimal design method of power system was proposed to solve the problem of lack in theoretical method for power system design and selection of electric fixed-wing quadrotor hybrid unmanned aerial vehicle (eHAV). The need of power system was proposed by calculating the thrust-to-mass ratio. The models of propeller design and performance calculation were established using propeller and rotor theories. The brushless permanent magnet DC electric motor was modeled using statistic method and first order motor model. The relations of voltage and current between motor and battery were used to establish the battery selection method. A fully empirical model for battery discharge characteristics with voltage correction was used to calculate the endurance of eHAV. The optimal design flow of power system was established based on the matching method. The power system of an eHAV was optimized and selected. The results showed that the errors between the proposed rotor and propeller models and CFD method were less than 10%

and the fitting degree between the discharge model and the experimental data was greater than 0.97. The flight test showed that the error of endurance between the flight test result and the design value was less than 4%

verifying the correction and feasibility of the method of power system modeling and optimal design.