Firstly, we employ the Lotka-Volterra model to formulate the interaction of species in an intact coral reef system. The simulation results show that all species’ numbers fluctuate for a long time. Then, the numbers all reach a steady state, that is to say, the system achieves a balance. Then we use the amount of algae and faeces to calculate the five indexes of water quality, which is sufficient for the continuous healthy growth of coral species.