Abstract: Based on the concept of system science and harmonizing development, the REES indices system and integrative assessment model was built up for the Neijiang city, and an assessment of ecological sustainable development level was delivered, after integrative assessment values of five level systems of Neijiang was calculated from 1990，1995 to 2004. Conclusions was drawn as follow: ① Neijiang city has been in the stage of weak sustainable development in the nearest 15a from 1990 to 2004; And the development of the city is of insufficiency in all when development connects with ecology; But from 2000 to 2004, society and economic system of the city had been put into fast developing stage, which betrays the response to West Development. ② The system of methods above, while being applied to assessment of regional ecological sustainable development level, possesses hiberarchy clear, visual and intuitionistic characteristics, and accords with fact; Selecting and using criterion values of indices, as well as comparing with time-sequence data in assessment, has the merit of organically linking space with time.