Gushanzi basic-ultralbasic rocks locate in the northern margin of North China Craton and the intrusions are mainly composed of hornblendite, gabbro and pyroxenite. The representative minerals, i.e. hornblende, pyroxene and spinel, are chosen for electron probe analysis and hornblendite and gabbro are chosen for major element, trace element and Sr-Nd-Pb isotope studies. Based on the data of electron probe the subdivisible mineral species and several geochemical characteristics are confirmed, which indicates pargasite with mantle-derived charateristic, diopside with Arc cumulates characteristic and Al-spinel only cumulating massively in pyroxenite. Petrogeochemistry and Sr-Nd isotope studies of Gushanzi ultrabasic rocks suggest the primitive magma assimilated little crust materials. It is proved that there is a relative high degree of magmatic differentiation for the low Mg#(0.44~0.55) and relative high LREE/HREE ratio(6.54~8.34). Meanwhile many evidences indicate Gushanzi ultrabasic rocks belong to type 1 enriched mantle for example the enriched large ion lithophile element LREE,Rb,Sr,Ba et al.,the deficient high field strength element HREE,Cr,Ni,Nb,Ta,Zr,Hf et al. and low Sr-Nd isotope ratio((87Sr/86Sr)ⅰ=0.70398~0.70430，εNd(t)= -1.60~-2.72). Gushanzi ultrabasic magma intuded in the the late Paleozoic sedimentary basin which lies in the southern Inner Mongolian Uplift. And geochemistry of the whole rock presents the characteristics of Arc cumulates and continental rift mamatic rocks. According to the geotectonic background and geochemistry characteristics we infer Gushanzi ultrabasic rocks formed in an partial extensional environment back off the continental Arc.