The expansion of triticeae crops planting area in Southeast China in the Southern Song Dynasty was a special phenomenon, which was formed on the basic of special social and economy environment. In the early Southern Song Dynasty, wheat, barley, buckwheat and other triticeae crops were widely popularized to the five southeast provinces, and wheat farming achieved considerable development. However, its prosperity was also flourishing, and its decline was also sudden, in the middle and late Southern Song Dynasty, triticeae crops planting area rapidly shrank and stabilized as a supplement to rice cultivation. From the perspective of social and economic history, this paper, by observing the choices of interest groups such as the emperor, local officials, northern immigrants and southern natives, discusses the driving forces of expansion of triticeae crops planting area from four aspects: orders with rewards or punishments, relief loans and taxes, immigrants’ dietary preference, and triticeae crops’ relief function, and draws the following conclusions: The imperial court promoted wheat and barley through administrative and economic means: orders with rewards or punishments were the main contents of administrative means, while relief loans and taxes were the main contents of economic means. Northern immigrants’ pasta preference promoted wheat demand’s growth, especially in Liangzhe and Jiangnandong Province, but in Jiangnanxi and Fujian Provinces, the immigrants’ preference had not shaken the local rice eating habits. Triticeae crops were considered as “the grain that can meet the shortage of rice”, under the situation of tension between people and land, triticeae crops’ relief function was to promote rice farms to grow wheat and barley to cope with famine. To sum up, the expansion of triticeae crops planting area was the coupling of two driving forces: the promotion of the government and the dietary preference of immigrants, which were the external driving forces; the natural attribute that wheat and barley are harvested when rice is green, which was the internal driving forces. [ABSTRACT FROM AUTHOR]