Abstract: Based on field investigation and experimental data,the effects of soil and water conservation from different models of conversion of farmland to forest,were as follows:mixture of picea crassifolia and birch＞birch＞mixture of picea crassifolia and hippophae rhamnoides＞picea crassifolia ＞hippophae rhamnoides＞farmland,in hilly loess plateau in Qinghai province. The effects of biodiversity were as follows: mixture of picea crassifolia and birch ＞hippophae rhamnoides＞birch＞picea crassifolia ＞mixture of picea crassifolia and hippophae rhamnoides＞farmland. The effects of microclimate were as follows:mixture of picea crassifolia and birch＞birch＞mixture of picea crassifolia and hippophae rhamnoides＞hippophae rhamnoides＞picea crassifolia＞farmland. The study also showed the ecological effects were increasingly better as forest age increased.

Key words: hilly loess plateau, models of conversion of farmland to forest, ecological effects, biomass