Abstract: From 1986 to 1991,an intensive investigation on the disease index and ecological factors of larch needle cast was made in forest farms in Jilin Province.The data analysis of three hundred olots of larch plantations,Larix olegensis,revealed that the disease index of larch needle cast has a lot to do with ecological factors. The ecological model of larch needle cast was thus established as follows :y=15+21C11+6C12+9C13-23C21-15C22-C23+3C31+19C32+19C41+9C42+8C51-10C61(PAN SHI Model)y=21+16. 5C11+2.9C12+4. 9C13-22.6C21-15C22-1.7C23+0.4C31+15. 8C32+16. 9C41+7.4C42+7.9C51-9.5C51(JI LIN Model)where y stands for forest disease index and C11～C42 stands for ecological factors(level).According to the investigation and analysis,the occurrence and development of larch needle castis the integrated result of different ecological factors over a long period of time. From them odels,forecasting technique and ecological control for larch needle cast by afforestation were put forward.