Based on elastic-plastic plane strain theory,a plane strain finite element model(FEM) model,in which the mined-out areas were denoted using dead elements,was set up to simulate the forming and developing processes of the earth surface cracks and forecast the future development of the earth surface cracks during mining No.1 ore body in No.2 Mining Area of Jinchuan Nickel Mine.The simulated results such as the forming time and distribution of earth surface cracks were accordant with the practices.Through the analysis on the stress changes of rock during mining,the mechanical cause of the earth surface cracks was presented.