The human thermal comfort is influenced by many factors, and it is fuzzy, so it is a kind of stochastic fuzzy variable. So the evaluation of human thermal comfort is fuzzy also. and the method assessing the human thermal comfort with fuzzy mathematics is reliable. The factor affecting the human thermal comfort is analysed and predigested. Based on the analysis above,the methodology of assessing the thermal comfort is presented. The methodology resolves the decision_making continuum, so it lightens uncertainty of traditional method. The simulation results are compared with the Predicted Mean Vote index, and they are in good agreement. The study shows that the methodology of assessing the thermal comfort is reliable,and it presents a new approach for studying the human thermal.