Based on the load balance equation and the theory of hydrodynamic lubrication, the mathematical model of fluid dynamic of crankshaft system was established. The finite difference method and the iterative method were used to set up the numerical algorithm of this model. The influence of different factors including the mesh density, the relaxation factor and the boundary condition on the convergence of numerical simulation was investigated through a single cylinder engine. The results show that it’s best to mesh with circumferential grid number m=40，axial grid number n=20 and control the relation factor within 1.5～1.9 when solving the bearing lubrication characteristics. The JFO boundary condition is more precise than Reynolds boundary condition when the cavity pressure is high.