Through a systematic investigation into the ecological environment in alluvial plain area of Huxian county, it is suggested that the evolution of the ecological environment in this area is strikingly marked by human activities. Since the founding of the People's Republic of China, this area has undergone three stages: the rurality period before the year 1966, the degeneration period during the Cultural Revolution and the deterioration period under the circumstances of commodity economy. Though the change in nature is one cause of the environmental deterioration, human activities, especially the unreasonable development activities controlled by the government, are the dominating factor.