This article discusses the regional expansion problem of square check fabric. And an evaluating indicator is established for evaluating the regional expansion in fabric. All the square check fabrics tested in this paper consist of two different tightness weaves: one is loose weave and the other is tight weave. Firstly, prepare samples. The samples are weaved by using different kinds of ratio of loose weave to tight weave -i, weft density- Pw and grid width-b. Secondly, test the samples’ degree of expansion-X, and then calculate the expansion coefficient. Lastly, establish i-Y, Pw-Y and b-Y curve. The results show that, the expansion coefficient of the square fabric is increased with the increase of i; and increased firstly and then decreased with the increase of Pw ; but the change of the expansion coefficient of the square fabric is not obvious with the increase of b.