Abstract: The mudstones of Lower Permian Shoushangou Formation in Xi Ujimqin Qi of Inner Mongolia are well-developed source rocks in middle-south Daxinganling Mountains. With study on the characteristics of major, trace and rare earth elements in the mudstones, the paper analyzes the provenance, tectonic setting and weathering of Shoushangou Formation in depth. The ICV values of rock samples ranging from 1.15 to 1.57(averagely 1.33) show that the samples are basically not affected by secondary diagenesis. According to the A-CN-K triangular diagram, the mudstones are subjected to certain K-metasomatism. The CIA_corr values of 54.28-70.06 (averagely 65.33) are gained after correction, indicating the provenance has experienced primary-moderate weathering. Based on the analysis on the multivariable environment of major and trace elements, it is concluded that the argillaceous sediments of Shoushangou Formation are mainly derived from the felsic provenance, mixed with minus materials from the femic volcanic rock provenance, under the tectonic background of continental island arc. From the above, it is thought that the sedimentary features of the mudstones in the study area are attributed to the subduction of the Paleo-Asian Oceanic crust in early Permian.