Abstract: Based on the particularity of urban lake tropic state and the progress in lake ecosystem health evaluation, it was demonstrated that the relationship between ecosystem health index (EHI) and trophic state index (TSI) of response and non-response lakes was near quadratic function. The lake ecosystem elasticity coefficient was put forward, and the EHI was improved, which could better reflect the healthy condition of various lakes, and made the theory of Xu et al. more perfect and applicable. The improved EHI might be a quantitatively computable formula, which was closest to the healthy index concept defined by Costanza as yet and applied successfully in the ecosystem health evaluation of Xiamen Xinglin Bay.

Key words: Neural network, Grade program, Natural forest protection, Program illustration, Inclining factor