There are two kinds of factors, natural factors and human impacts, affecting cropland conversion and its eco-environment benefit. The human impacts involve three different levels of social-economic activity layer, policy and laws layer, and concept and consciousness layer. The different kind and level factors and their relationship are analyzed. Based on the survey of cropland conversion experiment in Ansai county, it can be seen that the three factors play very important roles in cropland conversion and its eco-environmental benefits. The authors suggest that more experiments on natural factors and human impacts should be carried out to make the conver ting rational for the purpose of better and longer eco-environment benefits.