Abstract: The sensitive indexes of drilling crumbs (K₁,△h₂ and S) and their critical value were the important basis to evaluate the risk of coal and gas outburst in working face. Through analyzing the relationship of three indexes, it gave the foundation and criterion for comparing the sensitivity of drilling crumb indexes in working face. For the criterion of S value, it proposed drilling hole expanding hypothesis and gave the expansion limit conditions. According to the statistics theory, it got the single index outburst incidence. Combined with fuzzy evaluating theory, it put forward the multiple indexes method to calculate the risk of coal and gas outburst in working face. This method was applied in experimental working face successfully.