Externally pressurized porous journal gas bearing is analyzed theoretically in this paper by introducing a flow model, in which the flow in the porous bushing is substituted by a flow in an assumed thin layer. The surface loading effect due to machining is taken into account as the increase of resistance to the gas flow from porous media to bearing clearance. The theoretical results are investigated experimentally, yielding a comparatively good conformity between them enough to certify the analysis. Then, the optimum design conditions of the externally pressurized porous journal gas bearing are obtained by theoretical calculations with considering the surface-loading effect.