The spilite-keratophyre sequence is formed of spilite and quartz keratophyre interbeddedly in Dashizhai Formation in Maodeng district of Xilinhaote, Inner Mongolia. The data suggest that the protolith age of Dashizhai Formation was about Early Permian. Rock assemblage, rock series and geochemical characteristics prove that the spilite-keratophyre sequence formed in a continental margin-arc and local rifting environment, evaluating from the cognate magma which is from the wedge mantle by fluid metasomatism.