This paper is the result of geological survey. Writers first discovered the basalt association at the bottom of the Middle—Upper Jurassic Tiaojishan Formation in the Xuanhua District—Zhuolu County area，Zhangjiakou City, whose age, geochemical properties, and geological significance requires to further research. This article conducts geological, petrological, geochemical, and isotopic chronological studies on the basalts. The SiO2 content of the basalt ranges from 39.49% to 49.74%, Mg # ranges from 28 to 65, and the Rittmann index （σ） ranging from 2.61 to 33.12. The basalt belongs to the alkaline basalt series and forms bimodal volcanic rock combination with the overlying trachyte, indicating that the early volcanic rocks of the Tiaojishan Formation were formed in a continental plate tensile environment.This set of basalts is a geological, petrological, and tectonic study of the basaltic magma underplating of the neutral volcanic rocks of the Tiaojishan Formation.