Abstract: Tangshan mine, belonging to Kaiping coalfield, is located in the northwest wing of Kaiping syncline, and its structure is very complex. In this paper, the entropy function is used to evaluate the structure complexity of the ninth coal seam in southwest section of Tangshan mine. The bigger the entropy value is, the simpler the structure, vice versa. Compared with fractal and fractal dimension, the result shows that areas with complex structure are mainly located in the west, north and east boundaries of the ninth seam, and the structure is relatively simple in both sides of the Lingzi anticline. It is concluded that the results of entropy are more reasonable because statistics and calculation are conducted separately for different faults and the important structure(folds).