Abstract: The issue of grain production has always been the focus point of governments and academics. In the paper, we explore the impact of land fragmentation on grain production. Taking the field survey data from farmers in Yancheng and Xuzhou, top two cities of crop yields in Jiangsu Province, as examples, the paper establishes Trans-log function model to weigh the existence of returns to scale. By calculating yield flexibilities of input factors with linear index and logarithmic index of land fragmentation respectively, the paper adds the output elasticity to get the coefficient of returns to scale. Then we get a number which does not differ significantly from 1. The result shows that there is no obvious increasing returns to scale in general when considering the effect of land fragmentation. And the output elasticity of land which is around 0.8 means that land is still the most important factor of production. Furthermore, land fragmentation will do harm to returns to scale of crop production, but it has both positive and negative impacts on grain yield in different regions. So, it is proposed that on the premise of promoting the transfer of rural surplus labor, government should pay more attention to the negative effects of land fragmentation.