Abstract: A comparative study on the water-heat conditions and meteorological and hydrologic factors of the forest vegetation in different elevations of the south slope of Laoshan mountain in Tianlin county of Guangxi was made from 1982 to 1991. In the study, the characteristics of the vertical changs in the waterheat cinditions of the mountain was revealed and the regression models on the relationships between these meteorological and hydrologic factors were established. In this paper, we will describe the role that forest plays in improving climate and conserving water resource, reducing runoff and preventing soil erosion etc. in this region. All the conclusions show that the forest in the south slope of Laoshan mountain plays an important role in safeguarding the ecological balance in the region.