Abstract: The modern propeller lifting surface method has been applied to calculating the performance of Ram Air Turbine,and a single layer vortex model is adapted to the blade,the wake is modeled to rigid cylinder wake coincided with Goldstein hypothesis.A numerical calculation for a model of Ram Air Turbine shows a good agreement of the coefficient of wind power utilization with its experimental data at both small and large loading.The distributions of induced velocities and circulation are reasonable.