Gas accident is one of the most common accidents in coal mine in china. This paper argues that the gas dangerousness is determined by many factors which are difficult to quantitative risk, and deems these factors are quantified and fuzzy comprehensive evaluation, comprehensive evaluation, which are benefit evaluation and master the coal mine’s gas safety level, and determine the safety investment direction and improve the benefit of safety investment that will reduce the coal mine gas occurrence probability, so as to reduce and avoid the happening of coal mine gas accident. The basic steps: first, to analyze and master all kinds of gas accident reasons; Second, to determine the assemble of the gas risk factors evaluation, determine the evaluation grade assemble; Third, to proceed the single factor evaluation, determine fuzzy relationship matrix and the fuzzy weight vector of evaluation factor, and to choose the appropriate composition operator, vector analysis with the result of fuzzy comprehensive evaluation; Finally, people will take corresponding measures to prevent according to the result of evaluation that shows safety weaknesses.