The model of thermoelastohydrodynamic (TEHL) analysis of a transmission gear in a fuel cell bus was developed. The influence of rotating speed on the frictional pair was investigated numerically on the base of the mathematical model. The pressure field, the temperature field, the oil film thickness were calculated under different rotating speeds. It is shown that the worst lubrication in the tooth root occurs and the minimum film thickness increases with growth of the rotating speed. The temperature of lubricant is up to 140oC at 4000rpm.