Abstract: The effection of the Chamaecrista.rotundifolia on the growth of the fruit trees and ecology of the red soil region in mountainous orchards was studied in this paper. The results showed that there was a decrease of 1~5℃ in the ground temperature, an increase of 3.79%~5.98% in soil moisture content and the increases of 293% and 213% for available phosphorus and kalium between the grass planting and clean culture in different soil layer during the high temperature season. The contents of bacterium and nitrogen fixing bacterium increased as 64 and 57 times and there were increases of 6.9% and 1.8% for the fruit yield and per fruit weight. The contents of total soluble solids and cane sugar increased as 3.3% and 11.5%, but there was a decrease of 8.4% in the total acid. Compared to the clean culture, there were decreases for the runoff coefficient and average runoff amount.