The Mesoproterozoic Changzhougou Formation is the first set of sedimentary cover on the metamorphic crystalline basement of the Yanshan area in the northern margin of North China Craton. It unconformably covers all kinds of Neoarchean gneiss. Based on the field geological survey, grain size analysis and geochemical analysis test were carried out on the sandstone of Changzhougou Formation, to disclose the paleoenvironment, paleoclimate, material source, tectonic environment, and basin properties during this period. The results of rock assemblages, sedimentary structure, and grain size analysis indicate that the sedimentary environment evolution of Changzhougou Formation is alluvial fans, braided rivers, and clastic tidal flats, from bottom to top. The geochemical characteristics of sandstones in Changzhougou Formation are characterized by high SiO₂, Al₂O₃, K₂O, and low TiO₂, Fe₂O₃, FeO, and MgO contents with high maturity. The chemical alteration index (CIA) varies from 52.00 to 73.23, and the chemical weathering index (CIW) ranges from 93.04 to 98.68. Due to the influence of potassium replacement, combined with A-CN-K diagram, Th/U-Th diagram, and paleoclimate discrimination diagram, the provenance may have experienced strong weathering, implying warm and humid paleoclimate. The ratios of Cr/Zr, Th/Sc, Ba/Sr, Rb/Sr, and La/Th-Hf diagrams indicate the provenance of Changzhougou Formation from the upper crustal environment, and the sediments were sourced predominantly from felsic rocks. The discrimination diagram of the tectonic setting shows that the sandstone of Changzhougou Formation was formed in the craton basin, that is, the Yanliao Aulacogen might be produced in the internal rift of the craton. In addition, the ratios of Tb/Yb, La/Sc, La/Th, and Th/Sc indicate a few obvious mantle materials in the sandstones. Therefore, the Yanliao Aulacogen is presumed to be the coastal-epicontinental sea formed on the continental crust basement of the North China Craton, not to the extent of continental crust rupture and oceanic crust occurrence.