Abstract: In order to improve the accuracy of the evaluation of geological structure complexity of 8^th seam in Luling mine, on the basis of the qualitative evaluation, four evaluation indexes were selected, they were fault density, fault strength, fault strike impact index and fold plane deformation coefficient. Then the grey fuzzy comprehensive evaluation method was used to evaluate the geological structure complexity of 8^th seam quantitatively. Four types and their distributions of structural complexity were obtained, which were respectively simple, medium, complex and extremely complex. The above evaluation results are basically in accord with mine actual situation, and their validation is reasonable, this provides a scientific basis for mining of the 8^th seam.