Abstract: Through simulation of the evolution of natural eco-environment of a watershed and comparison of the findings with the actual situation of the Chaohu basin,a comprehensive exponential formula is put forth for evaluating eco-environment in Chaohu basin.By setting up benchmarks for eco-environment indices in the formula and optimizing undetermined parameters in the formula with immune arithmetic-taboo search(ITS),the modified eco-environment evaluation exponential formula becomes simple,easy,practical and applicable.Evaluation of the eco-environment of the Chaohu basin,using the simplified model demonstrates that the overall eco-environment quality of Hefei City and the Chaohu basin is of Grade III,just acceptable,while that of Chaohu City and Liu′an City are poorer,which is in good agreement with the reality and the results of several other models.The formula should be considered as a useful tool for regional eco-environment management.