The stateofart of the researches on the againstinrush safe thickness of rock strata in karst tunnels is summarized. The advantages/disadvantages of and the relationship among the qualitative analysis method, the semiquantitative analysis method and the quantitative analysis method are analyzed and compared. The characteristics, inadequacy and development trend of the researches on the againstinrush safe thickness of rock strata in karst tunnels are discussed on basis of relevant research results. Due to the complexity and limitation of the analysis method used at present, the concept of fissure concentration influence factor is proposed and the standard for the value taking of the fissure concentration influence factor is provided. The equivalent elastic modulus and the equivalent Poisson’s ratio of the againstinrush safe thickness of rock mass are evaluated on basis of the proposed concept. Finally, a formula to estimate the againstinrush safe thickness of rock strata of karst tunnels on basis of the geological investigation data is obtained. The formula has been used in engineering cases and the rationality, effectiveness and feasibility of the formula has been verified. 