Abstract: Some reefs of Middle Carboniferous were discovered in Taizi River ba}tn. Located in Xiaoyu limestone bed, they emerge intermittently in a row on the surface, extending east一westernly 16 kilometers. They are situated in the Niutnaoling, Chigou and Yaoziyu of Benxi. The reefs are very abundant in organisms. The principal builders are Chaetetes penchiensis and Arachnastraea manchurica. Some algae also stabilized sediments by trapping and binding in the process of buildup. Atcessory organisms are Brachiopods, Bryozoans, Sponges, Crinoids, Foraminifera, Gastropod, Ostracoda,etc. The process of buildup is very simple. At the early stage, the non一typical bioherms were formed by algae on the organic bank. At the middle stage, become principal builders, Chaeuus penchiensis colonies and Arachsiastraea manchurica colonies laerally linked into thick board skeleton, which covered carbonate sediments, forming strong framework of reefs. At the late stage, the principal builders disappeared rapidly, and then Crinoids began to baffle sediments helpeds disappeared rapidly, and then Crinoids began to. baffle sediments helped by algae. In the end, the organisms were not able to buildup bioherms and the process of buildup stopped. The core of reefs may be divided into three microfacies in the area. They are; (1) Bindstone microfacies;(2) Bind一coverstone microfacies;(3) Bind一bafflestone microfacies. These reefs being discovered have extremely similar composition of organisms, type of buildup and character of framework in Taizi River basin. These bioherms occur in an uncontinous belt, in line with the direction of the regional sedimentary facies belt. Therefore it is considered that these bioherms belong to one fringe feef system.