Kulehu ophiolite located in South Tianshan Mountains consists of two groups of basalts characterized by different geochemical types. The ∑REE(24×10-6 ～28.36×10-6),(La/Yb)N (0.35～0.37), Zr/Nb (39.91～95.12), Ta/Nb (0.07～0.09) and εNd(t) (8.85～12.25) values of the first group indicate that their mantle sources have been subjected to intense depletion, similar to things of the source of N_MORB. Furthermore, the enrichment of LILEs and the depletion of HFSEs, especially the appearance of Nb and Ta negative anomalies, show the affinity of this group to island arc tholeiite (IAT). On the contrary, the ∑REE (56.38×10-6～101.29×10-6) and (La/Yb)N (0.96～1.36) values, the contents of incompatible elements (REEs, LILEs and HFSEs) and the appearance of Nb and Ta positive anomalies all show that characteristics of the second group are between E-MORB and OIB, more close to E-MORB. TheεNd (t) (8.39), Zr/Nb (9.74～1094) and Ta/Nb (0.06) values are similar to those of E-MORB, suggesting that the mantle source of the second group is fertile relative to that of the first group. According to an integrated analysis of geochemical characteristics of these two groups of basalts, Kulehu ophiolite should have been formed in a back-arc basin setting. The first group of basalts, which have obvious SSZ features, are products of partial melting. They were formed at the early stage of back-arc basin, being products of the depleted residue of MORB-source mantle following earlier melt extraction. With the evolution of the back-arc system, mantle counterflow resulted in the formation of a relatively fertile mantle, and the upwelling of this mantle beneath the spreading ridge of theback-arc basin and the partial melting resulted in the generation of the secondgroup of basalts. The age of Kulehu ophiolite corresponds with the subduction age of the South Tianshan Ocean, and the formation of Kulehu ophiolite might havebeen related to the subduction that induced the back-arc extension of this ocean in a period from Late Silurian to Early Devonian. 