Abstract: Abstract: As an important grain production base of China, Huang-Huai-Hai region is of great significance for the steady grain supply of the country. Under the strategic background of regional cooperative development, the spatial externality of grain yield per hectare has attracted increasing attention. In order to investigate the spillover effects of grain yield per hectare at county level, this study focuses on the 347 counties of Huang-Huai-Hai region by Markov Chain method and Spatial Markov Chain method, and reveals the spatial spillover effect of grain yield per hectare at county level during 1980-2010 as well as the influential factors of the differentiation of grain yield in 1995 and 2010. And the results show: 1) During 1980-2010, the type of grain yield per hectare at county level in Huang-Huai-Hai region transfers in a gradual and smooth way, with a low probability of large-scale crossing. 2) During 1980-1995, the likelihood ratio statistic is 52.198, passing the Chi-square test with the significance level of 0.01, and is 55.147, passing the Chi-square test with the significance level of 0.005 during 1995-2010. That is to say the regional background type exerts significant impact on the type shifting of grain yield per hectare, and it's more significant in the second stage. The growth of grain yield per hectare of the counties at medium-low or medium-high level is similar, while the counties with high yield and low yield under the action of the regional context, gradually change toward middle type. Taking the counties adjacent to the high grain yield for example, their grain yield types per hectare will have a relative high possibility to increase, and vice versa. 3) In the aspect of spatial pattern of evolution, the type of grain yield per hectare tends to increase in the plain, and reduce obviously in the municipal districts and the coastal area. However, the type of grain yield per hectare in Jiangsu, Henan and Shandong Province gradually transfers to be stable. 4) Variations like grain yield per unit area in the last stage, average net income of peasant, industrial structure and ratio of effective irrigated areas have great impacts on the differentiation of grain yield per hectare at county level. And the influencing direction and degree of the factors in 1995 and 2010 are significantly different. In 1995, grain yield per hectare in the last stage, average net income of peasant, ratio of effective irrigated areas and industrial structure have passed the test of the significance level of 0.01, separately, and these indices are significantly positive to promote the grain yield; in 2010, the index of grain yield per hectare in the last stage, average net income of peasant and plant structure goes through the significant test, and the significance level is 0.01, 0.01 and 0.05, respectively. Except the average net income of peasant, the rest both play a positive role in promoting the overflow yield. These results can provide scientific ground for the optimization of grain production and policy-making to increase the grain yield per hectare in Huang-Huai-Hai region.