In this paper, some analyses had been done by combining theory with practice based on a case study of a village which is located in Xi-Hai-Gu region, the very well-known poor region in our country.Soil and water loscaused by improper land use as usually saying, but why people do not use their land properly even today? The analysshow that. firstly the key problem refers to the population capacity of environment in an area; secondly, the central link is man-land relaticnship in land use, from which the equation, m_i=a_i×p_i can be summarized and it also predicates the population capacity of an area to be limited; and thirdly a perfect model of comprehensive controlling may be reached by two steps, the first is planting grasses, shrubs and trees and the second is controlling with engineering.