There is a threshold pressure gradient in the flow of fluid in low-permeability reservoirs. Based on the non-Darcy flow theory，a new computing method of natural depletion oil recovery considering the threshold pressure gradient in different flow forms was analyzed. The calculating formulas for depletion oil recovery of the vertical well，fractured vertical well，horizontal well，and fractured horizontal well in the low-permeability reservoir were developed. The effect of each parameter on the depletion oil recovery was discussed while applying the formulas to real cases. The results show that the de? pletion oil recovery decreased linearly with the increase of threshold pressure gradient. The oil recovery of the vertical wells is very sensitive to the threshold pressure gradient，the horizontal well is less sensitive，and the effect for the fractured horizontal wells is the weakest. The depletion oil recovery and the one per unit pressure drawdown increases with pressure drawdown linearly and in a gradually slower manner respectively. The depletion oil recovery of the fractured vertical well increases with the half fracture length，but the effect decreases gradually. Half fracture length is more sensitive than fracture space to the depletion oil recovery in the fractured horizontal wells. There is optimized half fracture length. It is recommended that the low-permeability reservoir with large threshold pressure gradient under depletion development should be developed with hydraulic fracturing.