Abstract: Dendrolimus punctatus Walker is one of the forest insect pest which does the greatest damage to the forest in China and is widely distributed over thirteen prov inces and one autonomous region of Guangxi, Guangdong, Fujian, Sichuan, Hunan, Jiangxi, Zhejiang, Henan, Hubei, Anhui, Jiangsu, Guizhou, Yunan and Taiwan with a yearly infected area up to 20-40 million mu, so it is of great significance to make good quantitative forecasts of Dendrolimus punctatus Walker, in order that comprehensive measures could be taken to eliminate it.The application of computerised techonology to the quantitative forecast of Dendrolimus punctatus Walker has now just begun in this country. In this paper, with digital computers and by the two-siage discrininant analysis, relationship between the incidence of Dendrolimus purciatus Walker and the weather factors is studied. According to the sieving standard of the program, primary meteorological factors influencing the incidence of Dendrolimus punclcius Walker are automatically sifted, which constitute discriminant functions that can be used as mathematical models for forecast and accordingly incidence of the future Masson-pirie caterpillar can be estimated (divided into 4 quantity classes; very low, low, high and extremely high). The method of discriminant analysis in the quantitative forecast by computerised means has been applied to the data from Lianjiang County, Fujian Province and Anji County, Zhejiang Province. The mathematical models used for forecasting the incidence of Dendrolimus punctatus Walker in Lianjiang County are as follows:The mathematical models used for forecasting the incidence on Dongfeng Farm in Anji County, Zhejiang Province are:Calculations show that these mathematical models reach a reliability of 84.6 -100% in the historical probability and good results can be obtained in forecasting by using them.