In this paper, the metazoan framing reef of Carboniferous is taken as an example The relationship between crinoids and frame building corals in reef communities and the function of crinoids in reef building process are discussed according to reef growth and community ecological interactions It demonstrated a relationship among the biological factors in reef ecosystem It is found that the crinoids dominating communities contribute the initialization of corals in primary stage of reef development; while in reef building process, an environment controling competition is developed between crinoids and frame building corals, which leads to an increase in one and a decrease in the other in biomass Environmental changes resulted in the death of corals and the break of reef growth, leaving only crinoids, and competition disappeared The crinoids provided bioclasts for the reef continually, which covered the coral reef framework and protected the reef to some degree