Abstract: The extended finite element method combined in ABAQUS software is used to simulate the propagation of crest cracks of an earth core rockfill dam. For the simplified plane FEM model with initial cracks, the conclusions are obtained as follows: the main reason leading to the crest cracks is the uncoordinated deformation, and the effects of wetting deformation aggravate the uncoordinated deformation. The dam crest cracks are mostly distributed at the downstream side of core wall, and the direction is toward the downstream side within a certain depth and with about 45° to the horizontal surface. Besides, the initial length has little influences on the propagation direction of cracks. A plug-in for calculating the length and opening of the crack is compiled. Taking the crack closer to the center of core wall for an instance, the average propagation length of cracks is 2.5 m, and the average opening distance is 0.18 m. The closer the initial crack is to the center of the core wall, the larger the length and the opening of the cracks are. It is recommended that the quality of the middle part of dam core should be guaranteed during the design and construction periods.