Abstract: This paper expounds the mathematical theory of Monte Carlo method and the selection of mathematical model, and analyzes the mathematical model of fitting the parameters of resources by taking k1 steep inclined coal seam in the south of Zhonglianshang Coal Mine for example. The tests indicated that the gas content obeys Beta PERT distribution, coal thickness obeys lognormal distribution and gas-bearing area follows gamma distribution. Using the simulation parameters, we estimated gas reserves of k1 coal seam in Zhonglianshan South Mine. The calculation method provides a desired value of CBM reserve with a certain degree of credibility. Especially in the steep coal seam, it can reduces the impact of subjective factors to the maximum extent, and provide objective, reliable and reasonable reserve values.