We have little information on the fatigue strength of a compression plate in fixation of a fracture under weight-bearing.Seven models of femoral shaft fractures were prepared with 3 pairs of fresh adult cadaver femora and fixed with the trapezoid compression plates. The strain gauges were placed at the edges of the central screw holes on the surface of the plate.In combination with the simulation electric measurement and the fatigue calculation,it was suggested that losing the stability of a fracture was the internal factor cutting down the fatigue strength of the plate. The fractured fragments should be fixed stably and the functional exercises should be directed reasonably by the safety factor of the plate, which may be helpful to improve the safety of applying the plate.