Abstract: Ecosystem function refers to the ability of an ecosystem to maintain its own or other ecosystem health and to provide products and services directly or indirectly for human beings. The objective evaluation of coral reef ecosystem function is significantly important to realize the effective protection and sustainable utilization of resources. This paper analyzes the generation mechanism of coral reef ecosystem function based on the concept and connotation of ecosystem function. It provides a quantitative overall evaluation on the health and function of coral reef ecosystem integrity of Xuwen National Coral Reef Nature Reserve in 2006 and 2016 survey data using the coral reef ecosystem function evaluation method based on the coral reef ecosystem function index (CREFI). The results showed that the CREFI in Xuwen National Coral Reef Nature Reserve in 2016 was higher than that in 2006, which was mainly due to the decrease in the mortality rate of coral reefs and the obvious increase in the species of herbivorous fish. The evaluation results of CREFI with clear goals and theoretical framework of application, available and scientific evaluation data can clearly reflect the temporal and spatial variations, the healthy status and function stability of the coral reef ecosystem function. It also provides a reference for coral reef ecosystem management and decision-making as a quantitative evaluation model of coral reef ecosystem function.