Abstract: Chencai Group is the main Precambrian basement at the northwest edge of Cathaysia. Researchers have focused on the study of Chencai Group over a long period of time because of its abundant information about the evolution of Jiangshan-Shaoxing suture zone. The authors divided the Chencai Group into banded biotite plagiogneiss, monzonitic granite and mafic dikes which intruded into the plagiogneiss. The zircon ages of biotite plagiogneiss are mainly concentrated around 1800 Ma, 700 Ma and 220 Ma. The age of about 1800 Ma is the peak value of inherited zircon in gneiss. The age of about 700 Ma is the minimum formation time of gneiss protolith, and the age of about 220 Ma is the metamorphism age of gneiss. Monzonitic granite crystallized at 220Ma. Metamorphism and magmation resulted from the tectonothermal event during Indosinian period, which responded to the Indosinian orogeny of South China.