The fluid flow is non-Darcy flow in a tight reservoir. A startup pressure gradient is necessary for the flow in the tight reservoir porous media. The numerical simulation technology and software are mostly based on the Darcy seepage and could not effectively simulate the non-Darcy flow for tight reservoirs. In this paper, considering the complexity of the tight reservoir, the non-Darcy flow and the nonlinear characteristics, the oil-water two-phase compressible flow continuity equation, the motion equation, the state equation and the auxiliary equation are derived, to establish the oil-water two-phase non-Darcy flow mathematical model for the reservoir. The startup pressure gradient is considered in this model. The model is discretized for the low permeability and the strong heterogeneity in the tight reservoir with the finite element to be applied to complicated boundaries, high order differential equations, and weak grid orientations, with a high calculation precision. The numerical solution equation for saturation and pressure is obtained. The method is verified by examples.