The Reynolds equation was discretized to a linear system of equations by medium difference scheme.The solutions of difference equations were obtained by Neumann lemma.According to the Taylor formula,the error between analytic solution and accurate solution of medium difference scheme was calculated.The relationship between the error and mesh number was analyzed.A lower bound of complexity which was O(N 3) was obtained by the infinite norm.The relationship of real error,iterative error and mesh number was analyzed by computer test and the infinite norm.The result shows that the real error is much larger than the iterative error.The ratio of real error and iterative error presents a strong proportional relationship