The formation age, diagenetic, and tectonic attributes of a set of medium- deep metamorphic rock series exposed in the Longquan area, southwestern Zhejiang Province, an important component of the Cathaysian massif, remains controversial. Based on petrogeochemical studies of the metabasites from the Longqun metamorphic rocks, the diagenetic tectonic environments of these rocks can be divided into at least two types. Type Ⅰ rocks have the same REE distribution curves and spider diagram of trace element with IAB. The trace element ratio and discrimination diagrams indicate that these rocks were formed in an island arc setting which was related to subduction. Type Ⅱ rocks have the same REE distribution curves and spider diagram of trace element with OIB. The trace element ratio and discrimination diagrams indicate that these rocks were formed in a within- plate tectonic environment which were not relevant to the subduction. The rocks symbiosis of different tectonic attributes proves that the original Longquan Group is a subduction accretion complex. The zircon U- Pb dating of metabasites yielded the peak metamorphic ages between 404~402 Ma. This provides new data for reevaluatingthe tectonic attributes of the Lishui- Yuyao fault zone, the establishment of the regional tectonic framework, and the further analysis of the material composition and structure of the Cathaysian orogenic system.