In this study, effects of surface roughness on the load carrying capacity of the rotor-bearing system supported by externally pressurized air bearing are theoretically investigated. Air flow between rotor and bearing surfaces, is modeled using Reynold's equation. In this model, film thickness function which is defined gap between rotor and bearing, is described with surface roughness. In order to obtained pressure distribution between rotor and bearing surface, Reynold's equation is solved with Differential Transform & Finite Difference hybrid numerical solution method and load carrying capacities is calculated. In order to analyze effect of the surface roughness on the load carrying capacity of rotor-bearing system supported by externally pressurized air bearing, an algorithm is developed in Matlab environment and it is simulated for different bearing geometric parameters and rotor angular velocities.