Abstract: The development characteristics of mini-type structures in the roof of No.3 seam in Yanzhou coalfield are discussed,and the emphasis of discussion is about the optimized orientation of minor faults.Then four groups of faults in the action of stress and their correlations are analyzed.Finally a conclusion is summarized:there are different influence on the seam's roof stability because of the different properties,the different combination types and the different positions of mini-type structure.