A quasi-static wear model for spur gears is proposed based on Hertz’ theory and Archard's formula to investigate the wear characteristics of tooth surface in real operation conditions. The numerical simulation reveals that the wear depth distributes evenly along the tooth lead while varies along the tooth profile. The surface wear depth claims its minimum value at the pitch circle and reaches its maximum value near the tooth root of the pinion. The effects of load level and cycle number on wear depth are further investigated to indicate an approximate exponential function of wear depth with respect to the two factors. This implies that the effects of load level and cycle number on gear wear must be considered during a gear design aimed at slow wear and long life-span. Finally,the effects of mesh misalignment and micro-geometry modification on gear wear are explored in terms of wear depth with respect to load distribution of tooth surface. The exploration finds that the wear depth distributes inconsistently when misalignment increases. Hence,it is highly recommended to control the mesh misalignment to improve the load distribution and reduce the wear. Meanwhile,by adopting proper micro-geometry modification strategy,the wear depth of the gear surfaces can be reduced greatly.