Four kinds of fatigue cracks are found in a suspension bridge with orthotropic steel deck. Finite element analysis was conducted to investigate the reason of fatigue cracks originated from the cope hole in the transverse crossbeams. The stresses surround the cope holes in the crossbeam are calculated under vehicle loads which are imposed on scheduled positions on the bridge deck. Then the relationship between the peak stresses surround cope hole and the loading position is acquired. There are 2 areas have the effects of stress concentration surround a cope hole, which are named area-A and area-B. The calculation results indicate that the peak stress in area-A is greater than the allowed fatigue stress-range under 2 million cyclic loads, and the actual position of fatigue crack detected in the bridge is coincide with the position of area-A.