Abstract: Yinhe rock mass is divided into two parts (north and south)by the Yinhe River system, and the age of southern rock mass (named Ercun rock mass) is different from that of the northern rock mass. The Ercun intrusive body is mainly composed of quartz diorite-tonalite. The LA-ICP-MS zircon U-Pb age of the quartz diorite is 444.0 ±4.6Ma, suggesting Late Ordovician. The chemical composition of the rock is relatively rich in sodium and poor in potassium, and Na₂O/K₂O ratio is higher than 1 (1.73~3.17), suggesting the potassium calc-alkaline series. The rocks are rich in LREE, depleted in HREE, and enriched with LILE, Rb, Ba, and K, with significant losses of HFSE such as Nb, Ta, P and Ti. Mineral composition and petrological geochemical characteristics indicate that it should belong to type I granite. The age and tectonic setting of the rock mass is similar to that of the Duobaoshan island arc igneous rock, which provides a new constraint for the southwest extension of the Duobaoshan island arc.