The intrusion of diabase sills in the shales of the Xiamaling Formation is extensively developed in Yanshan Mountain area of the northern part of North China Plate. Geochemistry of the diabase is characterized by high content of TiO2(1.70%~4.29%), low content of Al2O3(11.33% ~14.98% ), MgO(4.17% ~5.86% )and Na2O>K2O. In the K2O- TiO2- P2O5 plot, all sample points almost fall into the field of continental tholeiite. REE study indicates that the diabase is enriched in light rare earth elements with abundant rare earth elements, and the fractionation between LREE and HREE is not pronounced. Meanwhile, the chondrite- normalized distribution curve is right-oblique without obvious depletion of Eu. All these characteristics in combination with the Zr-Y, Zr-Nd, Zr/Y- Zr, Ti/100- Zr- Y × 3, Ta/Hf- Th/Hf and Nd/Zr- Th/Zr diagrams indicate that the magma was derived from the transitional mantle, and the diabase was formed in an intra-continent extension setting of North China Plate during the late Mesoproterozoic.