Abstract:This article mainly deals with the method of forest fire forecast in accordance with the establishment of the mathematical model. The mathematical model is established on basis of the study on the regularity of forest fire and fire danger grade determination after making both the study of the moisture content of combustible substances, the major cause of forest fire in the central area of Yunnan, and the analysis of not only the data obtained from many experiments on early spreading speed of forest fire, but also the historical data of forest fires and meteorological informations. After testing and analyzing this method in contrast with the way of fire forecast according to histoncal data, the result shows that this forecast method is an objective and scientific one with the characteristics of locality, practicality, and simplicity.Based on the above, this article also refers to the analysis of the atmospheric circulation and its physical quantity variation which is the cause of catastrophic forest fire in the central area of Yunnan. Thus the regularity of forest fire is figured out for forecasting catastrophic fires in this area.