An optimal design method of bilateral gas film stiffness was proposed to solve the problem of insufficient working stiffness of aerostatic guideway. The Reynolds equation of gas film pressure distribution was derived based on the gas lubrication theory and simplified assumption. The solution domain and boundary conditions of gas film flow field were discretized based on the finite difference method. Then the solution program of pressure distribution was compiled in MATLAB. The bearing capacity of gas film was obtained by integration, and the film stiffness was obtained by derivation. The influence of guiderail clearance, structure parameters of restrictor and air supply pressure on the static characteristics of guide rail was analyzed. It provides reference for the design and manufacture of aerostatic guideway.