On the strength of expounding the general situation of study area and the status quo of agricultural laborers in China, the changes of the scale and structure of them from 1985 to 2009 are analyzed by relying on the survey from farmers and statistical data from the government. The causes of these changes are analyzed from the aspects of rural farmland policy，birth-control policy, farmland marginalization and industrialization. Based on the study on the causes, the impacts of the changes on food production are analyzed from operation scale of household, the grain cropping area, the multi-cropping index and land productivity. The results show that the quality of agricultural laborers is decreasing form 1985 to 2009, which is characterized by the lack of middle-aged agricultural laborers and the aging of agricultural laborers. The causes of the changes include farmland policy, birth-control policy, farmland marginalization and urbanization. The shrinkage of agricultural laborers has grave effect on the multiple-cropping index. In addition, the land productivity is comprehensively affected by the scale and structure of agricultural laborers.