To investigate the fatigue performance of anchor plates, a composite beam cable-stayed bridge was taken for example in this study. A loading model in the new standard for steel bridge and the rain-flow method were applied to gain fatigue load spectrum, combined with a three dimensional finite element model to identify the typical structural details and fatigue stress spectrum of anchor plates. Initial surface cracks were imported in the typical details, and stress intensity factors of crack tips were calculated. The stress intensity factor and crack size were regressed by substituting in Paris formula, which were integrated to gain the fatigue life of typical structural details. The assessment of fatigue life for anchor plates based on fracture mechanics was then established. The results show that the fatigue life for anchor plate based on fracture mechanics is over 100 years, satisfying the requirement of design and utilization; the crack is developed very slowly in the early time, but when it reaches 10 millimeters, 50% to 80 % of its fatigue life is consumed. Therefore, reinforcement should be timely applied to the anchor plates.