Urbanization in the Yangtze river economic belt is developing rapidly, but many ecological security problems have seriously restricted its high- quality development. This paper aims to integrate the advantages of the characteristic index method and the index system method and explain the new connotation of the symbiotic development of social economy and ecology. Based on the analysis of the interaction between urbanization development and natural ecology, we selected data from 11 provinces and cities along the Yangtze river economic belt from 2006 to 2017and used"drive- pressure- state- impact- response(DPSIR) "model, R clustering method and coefficient of variation method to determine the ecological security index and its weight. Then, the lotka- volterra symbiosis model of urbanization- natural ecology was applied to obtain stress index and comprehensive characteristic index with ecological economic connotation, to achieve the coupling of index and indicator, and further to deduce the basis for early warning of ecological security. Finally, the paper carried out an empirical measurement, and retrospectively analyzed the causes of ecological security problems according to the measurement results, and completed the reverse decoupling. The results show that: (1) The urban system of the Yangtze river economic belt developed rapidly from 2006 to 2017, especially the urban driving force was strengthened. However, the magnitude of the improvement of the ecological environment was not obvious, and it was in a long- term biased development mode. Under this mode, the urban system developed, but the ecological environment was damaged. (2) The ecological security pattern of 11 provinces and cities in the Yangtze river economic belt was significantly different, presenting a pattern of "high east- west, low middle". (3) Through the backtracking of indicators, we found that the unbalanced industrial structure development, over expansion of urban population, and occupation of ecological environment space by urbanization subsystem were main reasons for the ecological security problems in the Yangtze river economic belt.