The Beishan orogenic belt is situated in the juncture area of Paleozoic Kazakstan Plate, Tarim Plate and North China Plate. On the basis of survey result of 1∶50000 regional geological mineral resources, this study conducted analysis of the gabbro distributed in the Baijing area using LA-ICP-MS zircon U-Pb dating and geochemical analysis in order to understand Early Paleozoic tectonic attribute of the Baishan area. The results show that these grabbros have U-Pb ages of 498.9±24Ma and should be in Late Cambrian with detail ages of (498.9±2.4) Ma. Geochemical data indicate that the gabbros are low in SiO2(40.39%~53.62%), high in Al2O3(12.56%~19.26%), CaO (8.09%~10.93%) and Mg# value, and have high REE(6269×10-6～250.62×10-6), slightly Eu anomalies (δEu=0.82~1.28), enrichment in LREE and relatively depletion in HREE \[(La/Yb)N=4.89~16.94\]. Those rocks are enriched in LILE(Rb, Ba, K), and depleted in HFSE(Th, U, Nb, Ta), with the low Lu/Y(0.01～0.02), high La/Nb(1.04~3.39) and La/Ta(11.73~55.32). Geochemical diagrams show that the magma might originate from partial melting of the transitional lithospheric mantle, with significant crustal contamination during ascending process. Gabbro is characterized by relatively high TiO2(0.65%~1.98%), Nb(4.47×10-6~18.56×10-6), Ta(0.44×10-6~1.86×10-6), Zr(48.07×10-6~386.86×10-6), Hf(2.17×10-6~21.23×10-6), similar to those of the intraplate basalts. In addition，synchronous monzonite granite developed in the south of gabbro body, along with gabbro, contributes bimodal magmatic rock assemblage. All the characteristics above show that the gabbro formed in an intra-continent extensional setting. It can be future presumed that the late Cambrian witnessed no Paleo-Asian Ocean subduction but the expansion stage.