Abstract: The issues of population, grain, resource and environment in Loess hilly-gully region are now becoming increasingly serious, attracting more and more attention from scholars and government. Aiming to alleviate the pressure on grain security imposed by ecological de-farming there, potential grain productivity should be stressed so as to know how to exploit it. Ansai County was selected as the study area and potential photosynthesis productivity, potential temperature productivity, potential precipitation productivity and potential land productivity for main grain plants and the whole county were estimated by using mechanism methodology, and the degree of potentiality being exploited was calculated. Based on analyzing the restricting factors to increasing grain yield and exploiting its potentiality, the paper holds that people should build basic farmland extensively, add assistant energy input scientifically, adjust grain crop structure properly and increase science and technology contribution efficiently, in order to exploit grain potentiality further and settle down grain security problem there.