In order to research the bearing capacity change of the oil within viscous friction drive, by choosing a non inertial coordinate system, started from the hydrodynamic equations, the Reynolds equation of the oil within viscous friction drive were obtained. By using Rayleigh hydrodynamic lubrication theory, then pressure distribution of the oil under the radial groove was solved,and simulated. By comparing the simulation results with experimental results, it is found that both trends are consistent，but the theoretical data are somewhat higher than experimental data. In considering that the oil film within the viscous friction drive were not always sufficient everywhere, so the actual pressure value of oil film are always lower than the theoretical value. Within the viscous friction drive, the oil in the tank are more sufficient than that not in the tank, so to the oil pressure value, the former are more in line with theoretical value than the latter, but all of them are in line with the simulation results and experimental data. The simulation results can supply better guidance to the research of oil film bearing capacity. 