Abstract: Based on the investigation of farmers in Hubei and Shandong province, this paper explored the influential effect of land scale on farmer’s adoption of organic fertilizer, analyzed the moderating effect of tenure security, and discussed the mechanism through which land scale affect farmer’s adoption of organic fertilizer. Results showed that: (1)Land scale has positive effect on farmers’ organic fertilizer application. (2)Tenure security moderates the effect of land scale on farmers’ organic fertilizer application. (3)Cognition and ability of organic fertilizer application are mediating variables in the land scale-farmers’ organic fertilizer application relationship. (4)The mediating effect of ability of organic fertilizer application is larger than that of cognition of organic fertilizer application. This study enriches the theoretical interpretation of economic behavior in classical economics, and provides suggestions for motivating farmer’s adoption of organic fertilizer.