Abstract: The Early Cretaceous Jianmenguan Formation is a good formation to study the sedimentary environment evolution in Northern Sichuan Basin. The systematical study on its geochemical characteristics is significantly important for studying the provenance, tectonic background, ancient weathering and paleoenvironment of Early cretaceous Jianmenguan Formation. In this paper, the geochemical characteristics of major elements, trace elements and rare earth elements (REE) of the argillaceous rocks of Jianmenguan Formation were systemically analyzed. The results show that the argillaceous rocks of Jianmenguan Formation are rich in CaO,MgO, lack Al₂O₃,Fe₂O₃,K₂O,Na₂O,TiO₂,P₂O₅,MnO, are rich in Cr, Cs, V, and lack Sr, Nb, U, Hf. The total amount of REE(∑REE) ranges from 164.96×10^-6 to 234.35×10^-6. LREE/HREE is in the range of 11.77~15.87. The fractionation between LREE and HREE is obvious, and LREE content is higher than HREE, with a weak positive Eu anomaly. Based on the analyses above, Jianmenguan Formation is recycling sedimentary rocks from the same sources. Its source rocks are sedimentary rocks, and it may be rich in europium-rich minerals such as plagioclase and barite. The source rocks underwent moderate chemical weathering before sedimentation and K-metasomatisim during the weathering process. The climate during the sedimentary period of Jianmenguan Formation was warm and humid. Tectonic evolution characteristics of the source area appeared to have a transformation from the continental margin to the continental island arc.