Monte-Carlo method was applied to simulate the distribution of the contact fatigue stress and the contact fatigue strength of spiral bevel gear, furthermore, reliability was also simulated. The method solved the small sample problem. According to the analysis, the contact fatigue stress of the gear submitted the normal distribution, and the strength of the gear obeyed the lognormal. The reliability error of the contact fatigue was reduced with the increase of the simulation times. Sensitivity analysis has been made on the stress random parameters which probably impacted the contact fatigue reliability of the gear. Results revealed that the affection of mean is remarkable to the reliability of the gear. The standard error is relatively small. 