Abstract: A bioherm 15m in thickness is exposed at the top of Cambrian Changshan Formation in Jinzhou area, Liaoning Province. Macroscopically, the bioherm is made up of thrombolite and leiolite, and microscopically, it is mainly composed of dense micrites and different kinds of grains. There are different types of grains, such as calcified microbes, benthic oolites, oncolites, bioclasts and clots, in the inner part of the bioherm, which indicates complex microfabric of the bioherm. The surface of trilobite skeletal clastics encrusted by micrites shows constructive and destructive micritization. Bioclasts dispersedly distributed within the dense micrite reflect relatively strong binding during the development of the bioherm. Large quantities of pyrite crystals existent in the dense micrites demonstrate that the formation of dense micrite was genetically related to heterotrophy-bacteria activities. Together with pyrite crystals, all kinds of grains within the bioherm reflect complex microbial activities during the formation of the bioherm, which provides not only prerequisite for the study of microbial sedimentation but also an important example and clue for the research on different types of grains within the bioherm.