Abstract: By making parallel observations on the microclimate factors(including air and ground temperatures,the highest and lowest temperatures,relative humidity,wind speed and soil moisture) and the water content ratios of 5 combustible materials(i.e.litter,humus,green cover,shrub,and branches and leaves on the canopy) in Yunnan pine(Pinus yunnanensis Franch.) forests in Kunming area during dry seasons,the authors analyzed the correlativity of the microclimate factors acting on the water content ratios of the 5 combustible materials.After the observed data were treated on a computer by means of multivariate regression analyses,4 major microclimate factors corresponding to each combustible material were analyzed and screened so that the scientific basis of this study was provided to establish the equation for the forecast of forest fires.Based on the 4 factors-soil moisture,air temperature,ground temperature and relative humidity,which effect the water content ratios of the forest combustible materials significantly and reveal the basic relations between the forest environment and forest fires,fire hazard periods and various classes of fires for Yunnan pine forests and similar stands have been decided preliminarily.