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The methods of contact stress analysis and fatigue crack initiation prediction of gears are presented and applied to a pair of spur gears in a high speed diesel engine in this paper. The surface and subsurface stresses of the gear tooth is investigated using Hertzian theory and finite element method. The effects of friction and speed are analysed. It is found that friction will increases the von Mises stresses and change the shear stress cycles so that the surface pitting is more likely to form with the increase of friction. It is also found that the stresses of the points near the engagement and recess areas are very great, and with the improvement of speed the stresses fluctuate more severely and these zones become more dangerous and resulted lower fatigue lives compared with static contact conditions.