Abstract:The stability of macrocrack in engineering was analyzed based on LEFM(linear elastic fracture mechanics) model;and the crack tip¢s stress intensity factor was calculated by displacement direct method. In response to the problems whether crack tip must be subdivided with fine-mesh and nodes¢ displacement were used to extrapolate the crack tip¢s stress intensity factor and so on,the sensitivity of mesh size on crack tip¢s stress intensity factor was analyzed. The following conclusion can be obtained. (1) When using displacement direct method to extrapolate the crack tip¢s stress intensity factor,it must ignore the nodal displacement near the crack tip and use the far field one;(2) If the 1/4 edge middle node(singular isoparametric element) was used near the crack tip,it could also obtain the satisfied result even with the coarse mesh,which will greatly reduce the computing workload. These findings were verified by the analyses of a typical three-point bent beam with cracks and the horizontal cracks of Longyangxia gravity arch dam. Then,base on LEFM model,the horizontal crack¢s depth of Longyangxia gravity arch dam was forecasted.