The Halaha River and Chaoer River volcanic field (HC for short), middle of the Great Xing’an Range, is in the north of the North-South Gravity Lineament in eastern China. The volcanic rocks in HC, dominated by alkali olivine basalts in sodium series, are characterized by relative enrichment in large ion lithophile elements and light rare earth elements.  All data show that bsalts of HC have a garnet lherzolite mantle source, low degree partial melting (8%～15%)in which results in the primitive magma. Crystal fractionation of olivine and pyroxene from the magma is weak and seldom contamination by the crust rocks happens during the magma ascending,which resulting the volcanic rocks with high MgO content (>9%),Ni conten (>200×10^-6) and Mg value (60～70). Regional extension triggers asthenospheric upwelling, which may lead to the genesis of magma and subsequent volcanism.