Abstract: Rigid trailing vortex model consistent with Goldstein hypothesis is often employed in propelles lifting line (lift surface) calculation on the condition of light load,but presents certain errors on the condition of heavy load.Semi rigid trailing vortex model consistent with Theodorsen hypothesis extents Goldstein trailing vortex to heavy load condition.Application of Theodorsen trailing vortex model to ram air turbine lifting line calculation is discussed.A model ram air turbine has been employed to calculate.The results show reasonable distributions of trailing vortex pitch,induced velocities,circulations and blade element wind power utilization coefficient.Wind power utilization coefficient agrees well with experiments.