At present about 60% of ecosystem has been damaged and degraded severely, resulting in enormous ecological loss globally. The essential cause is the irrational utilization of ecosystem by humankind, so it is the key to Changing improper environmental performance of humankind so as to prevent ecosystem from being damaged. The quantitative valuation on the loss of ecological damage is an effective tool to guide human eco-environmental performance. In this paper, the concepts related to the valuation on ecological damage cost are introduced; uncertainties that might arise in the valuation on the loss of ecological damage such as area coverage of valuation, ecological damage quantity, borders of ecological damage cost and data support are analyzed; and the valuation approaches for the loss of ecological damage are also discussed. As a case study, the economic losses of ecological damage of forest in 2005 in China are valuated.