Abstract: The major elements and trace elements of the Guanmenshan syenogranite in Benxi area, Liaoning Province are studied. The characteristics of the major elements show that the syenogranite belongs to high-K calcium-alkaline series. The seagull-shaped chondrite-normalized REE distribution patterns suggest enrichment of LREEs and depletion of HREEs, with medium negative Eu anomalies. Trace element spider diagram shows that the rocks are enriched in large ion lithophile elements (LILEs, such as Rb, Th and K), whereas depleted in high field strength elements (HFSEs, such as Ta, P and Ti). The composition of trace elements in syenogranite indicates that the formation pressure of granite magma is less than 1.0 GPa, and the source materials exist in the depth of 30-40 km of the earth crust, belonging to thinned crust. The syeogranite was formed in the Early Cretaceous when the Liaodong block was in intracontinental extension environment.