Abstract: It is very important to forecast concealed geological structure for coal mine safety production. Based on characteristics of Ⅱ₁ coal seam gas drainage engineering in Guhannshan Mine, the mathematical model for the small structure of the test face is established by analyzing feasibility of the gas drainage engineering of through beds hole. Combined with the field construction data of gas extraction project in the test working face, by drawing the three dimensional surface diagram of coal seam floor, contour map of coal seam floor, trend surface residual diagram of coal seam floor and the contour map of coal seam thickness, we comprehensively determine that there is a small fold with the wavelength of 100 m, the axis direction of N58°W and the working face ruler between 150 m and 250 m. The actual situation of coal production is consistent with the theoretical prediction of the small fold, which gives an effective guidance during the process of the working face mining.