Abstract: The influence factors of coal and gas outburst are random, fuzzy, grey and unknown, the traditional evaluation method is difficult to balance the determination and uncertainty of evaluation indexes, which leads to the distortion of coal and gas outburst evaluation． To solve this problem, a comprehensive evaluation system for coal and gas outburst is established, and a new evaluation method based on unascertained theory is introduced; based on the comprehensive evaluation index of coal and gas outburst unascertained factors, the influence factor weight by AHP is determined; vector model is established by the impact factor of the unascertained measure vector；using confidence to describe the evaluation results, the level of coal and gas outburst is obtained．Evaluation of coal and gas outburst in Xinxing Coal Mine is carried out by using new evaluation model． The evaluation result is “safer” grade, which conforms to the engineering practice． The engineering example shows that the coal and gas outburst evaluation based on unascertained measure theory is accurate, reliable, high precision, and has high application value．