The numerical simulation technology of ultra-low permeability reservoir is the focus of scientific researchers in recent years.However, the nonlinear segment of the seepage curve of low permeability reservoir and the effect of starting pressure gradient on reservoir exploitation are not considered by commercial software.In this paper, the nonlinear seepage numerical simulation technology of extra-low permeability reservoirs is the main research direction,and the nonlinear seepage numerical model of extra-low permeability reservoirs is established.The self-made software was used to simulate and study the effects of nonlinear seepage on the numerical simulation of extra-low permeability reservoirs.The differences between Darcy model, pressure gradient model and nonlinear seepage model are compared.The sensitivities of the direction and oil-water phase of nonlinear seepage are analyzed.The simulation results show that the production of pressure gradient model is the worst, which exaggerates the formation resistance.The Darcy model does not consider the existence of starting pressure gradientand reduces the effect of formation resistance on seepage.The presence of starting pressure gradient in nonlinear model leads to an increase of seepage resistance,which increases production pressure difference and reduces well production.The results provide a theoretical method for the flow simulation and high-efficiency exploitation of extra-low permeability reservoirs, which have certain guiding significance for improving the recovery of extra-low permeability oilfields.