Abstract: In order to analyze the mixing performance of spacer grids with Computational Fluid Dynamics （CFD） method,the geometry model and mesh division of fuel assembly spacer grids are investigated systemically. Compared with the results of different geometry models,the spacer grids can be simplified as the structures of ribbon and mixing vanes only,without dimple or spring. And the exit length and entrance length are set as 250 mm and 230 mm,respectively. And the fuel assembly with only one pacer grid is to be researched. Through the effect of mesh on the calculation results,the method of mesh division and mesh quantity are confirmed. The entrance part and exit part are for the structured mesh,while the part of space grids is for the unstructured mesh. The total nodes number of whole research object is 1032258,and total cells number is 2601614,of which the spacer grids part is 75.8%. The following research of mixing performance of fuel assembly spacer grids with CFD method,will be performed on the base of geometry model and mesh size,which are confirmed in the research of this paper.