Abstract: The goaf effect formed by the large-scale underground coal mining will change ground gravity field. There- fore,it is of practical significance to inverse the evolution and characteristics of variation of the hollow above the coal mine goaf by ground gravity survey for the safety of coal mine and ground protection. For a long time,due to its small magnitude,this kind of gravity anomaly effect caused by coal mine goaf is neglected. Based on the Bouguer gravity the- ory,the author uses numerical simulation method to obtain ground gravity anomaly distribution characteristics of the goaf in longwall face,and establish the corresponding relationship between depth,width,thickness,mining boundary of working face and the distribution of gravity anomalies,use third-order compact difference scheme to acquire its first de- rivative curve. Different kinds of fitting methods are adopted to smooth the distribution curve of the ground gravity a- nomaly in the goaf,which is simulated by adding random errors of different sizes. Also,according to the peak point of the first order difference curve,the boundary position of the goaf is deduced,which provides the feasibility of using the gravity method to inverse the change of coal mine goaf under the existing technical conditions.