Agricultural land transfer has an important impact on grain production and food security, but whether it promotes the grain production or not is still unclear. This paper analyzes the relationship between agricultural land transfer and grain yield using the theory of "decoupling" and the survey data in Hunan province. The results show that: from 2005 to 2016, there was a decoupling relationship between agricultural land transfer and grain production in Hunan province, and the basic trend was expansionary negative decoupling, in 2010, 2013 and 2016, it showed strong negative decoupling, while it showed strong decoupling in 2007. It can be said that the transfer of agricultural land has not achieved the expected goal of increasing grain production. The reasons include: the information asymmetry in the transfer market of agricultural land, the low efficiency and profit of the transfer; the lack of scale management caused by "small-scale reproduction" existing in the transfer of agricultural land, which has not realized scale management; the "non grain and non agriculture" caused by transfer of agricultural land; the low level of socialized and organized services corresponding to the transfer of agricultural land.