Due to high viscosity，heavy oil shows the non-Darcy flow in porous media. The numerical simulation software based on the Darcy model fails to fully consider the influence of variable starting pressure gradients and pressure sensitive effect on oilfield production indicators. In light of the heterogeneity of actual reservoirs and pressure sensitive effect，the starting pressure gradient was converted into a variable related to fluidity and its directionality was taken into account. Then a mathematical model of variable starting pressure gradients was constructed for heavy oil reservoirs，which was discretized and linearized to solve pressure and saturation in a fully implicit manner. The pre-processing and post-processing modules of the simulator were connected to ECLIPSE for the numerical simulation of typical heavy oil blocks，and the simulator was applied to a field model to characterize seepage field distribution. The results demonstrate that the starting pressure gradient will reduce the water flooding swept area，aggravate the non-piston phenomenon and the inter-layer contradiction，and the pressure sensitive effect will impair oil displacement efficiency.