Abstract: Restricted by technique and means,there are some artificiality and localization in various original geological information and worked result gained from the exploration.Digital curved surface fitting is a new structural examination technique,it can construct ore basal shape by utilizing discrete data which gained from exploration,in order to improve the scientific factor in structural examination.By anglicizing mathematical model which fits surface fitting in floor of coal seam,researching No.4 coal bed of B section in south of Fengjigou,Ningxia municipality,the authors indicate that digital surface fitting can analyse and research coalfield structures effectively,and it offers a new way for studying coalfield structures.