Abstract: In this study, a citrate synthase gene with a length of 1 218 bp was cloned from Malus xiaojinensis Cheng et Jiang and named MxCS4. It was predicted that this gene could be translated into a protein with 405 amino acids. The expression level of Mx CS4 in leaf, root and phloem was higher, but in xylem was lower. When treated with low iron concentration(4 μmol · L^-1), the expression of Mx CS4 in root and new leaf increased first and then decreased, and in mature leaf decreased gradually. When dealt with high iron stress(160 μmol · L^-1), the expression of MxCS4 in mature leaf increased first and then decreased, and the expression in root and new leaf decreased gradually. Under the treatments of ABA and IAA, the expression of MxCS4 in new leaf, mature leaf and root all increased first and then decreased. Subcellular localization studies confirmed that the MxCS4 protein was localized on the cell membrane. The results of the transgenic test showed that overexpression of the MxCS4 gene increased the absorption and transport capacity of the transgenic Arabidopsis thaliana to iron and other metal elements, thereby increasing its tolerance to low iron and high iron.