With the further study of ecosystem, people begin to pay more attention to the services provided by ecosystems that have been ignored for many years and begin to use measurable methods to express the values of ecosystem service, so the evaluation of ecosystem service is taken into account and is becoming an advanced ecological issue in recent years; at the same time, as more and more ecosystems degrade, studies on ecosystem succession is becoming another hot pot and when ecosystems degrade, the ecosystem service changes too, but little previous research has been carried out about the change of ecosystem service value.
Based on the literatures, ecosystem services are classified into two categories: value of natural resources and the value of humanities. The value of natural resources included matter value (including food, material, etc.), ecosystem process value (including water purification, atmosphere regulation, etc.) and habitats value. The value of natural resources could be evaluated directly or indirectly, but up to now there are not recognized methods to evaluate the value of humanities（scientific research, education and tour, et al） because it is influenced by so many factors. In present paper, the natural resource value of the urban lake ecosystem services, Xiannv Lake as a case, during the degrading process was evaluated and some methods, such as, the market value approach, reforestation cost approach, shadow project method, surrogate market method, carbon tax approach, et al, were employed. Results showed that some ecosystem service values decreased quickly with the degradation of Xiannv Lake ecosystem, such as gas regulation (460,124 Yuan in 1999 and 8 Yuan in 2004) and environmental purification values (11480 Yuan in 1999 to 904 Yuan in 2004). Not all functions decreased with ecosystem degradation. Some functions such as water resources regulation remained unchanged because lake volume was unaltered. Yet other functions increased, for example, fish production increased from 152400 Yuan in 1999 to 241200 Yuan in 2004. The study has a significance for restoration of a degraded ecosystem. As a degraded lake is restored, ecosystem functions or services such as CO₂ fixation, O₂ release, and environmental purification services would increase significantly, but other functions may remain unchanged or decrease. The methods applied in this paper are convenient and widely used, but further improvement in the criteria and principles of evaluation, particularly for lake ecosystem services, is required.