Abstract: An important measure to ensure the national food security and improve the quality of arable land is to demarcate the prime farmland scientifically and reasonably. There are three types of evaluation units for delimiting prime farmland, mainly including administrative villages, plots and grids. Compared with the other two types, grid can not only break the constraints of irregular geographic data, improve the ability of data update and retrieval, but also integrate, share and use information resources, which is easy to locate in the space. In the current research field, the demarcation of prime farmland is generally carried out in a uniform grid environment. If using large-scale uniform grid, however, the area of small and scattered arable land will have a large error. Although using small-scale uniform grid can reduce the area error, there are other problems such as large amount of data and high redundancy. The advantages of non-uniform grid are obvious. Its data volume is far less than that of uniform grid, which effectively reduces the frequency of invalid data search. And, the efficiency of data retrieval and transmission can be improved. "Centralized and continuous, high quality" is the requirement of realizing the construction of prime farmland with high spatial standard. Therefore, the purpose of this paper is to establish a method to divide and express prime farmland by using arable land concentricity and arable land quality index with the non-uniform grid environment. Wenxi County of Shanxi Province is taken as the research area. The research methods of the paper are as follows: to construct non-uniform grid and multi-scale uniform grid with the help of Arc-Engine secondary development platform; Comparing the expression error of arable land area and the data amount of grid, and then analyzing the advantage of non-uniform grid in cultivated land expression. Focusing on the contiguous land and the quality of cultivated land evaluates the spatial distribution of cultivated land. The results show that the arable land is divided into permanent protection type, quality improvement type, key management type and reserve management type by the method of spatial superposition; On the basis of the connotation of prime farmland, demarcating and expressing prime farmland. Using non-uniform grid can not only reduce data redundancy, but also achieve small error expression of arable land information. The delimitation results of prime farmland in Wenxi County meet the requirements of "centralized, continuous and high quality". The area of prime farmland accounts for 83.22% of the total area of farmland, and the demarcation proportion conforms to the national regulations. The non-uniform grid can well express the spatial distribution of prime farmland. Obviously, this method is suitable for the demarcation of prime farmland and provides a new way for expressing prime farmland better.