The forest ecosystem around the city is constantly occupied upon, resulting in the degradation of ecosystem functions, which seriously threatens the urban ecological security. The concept of "the environment is valuable, the damage is liable, and all losses should be paid" is a solid institutional guarantee to solve the unreasonable situation of "enterprise pollution, mass victimization, government pays the bill", improve the quality of the eco-environment, and meet the people's growing demand for a beautiful eco-environment. And it is imperative to practice this concept and improve the quality of the urban ecosystem. Different environmental pollution and ecological destruction behaviors will have serious impacts on the natural environment, and for a complex ecosystem with a high degree of social-economic-natural combination like a city, the consequences of eco-environmental damage are also more complicated. Due to the complexity and integrity of the ecosystem, partial damage to the ecosystem will lead to the loss of the integrity of the ecosystem and the loss of various original ecosystem functions, so it is difficult to obtain full compensation. As the beneficiaries of urban ecosystem services are mainly people in urban areas, many of its service values are subjective. Therefore, the baseline confirmation, scope investigation, physical quantity accounting, and value analysis of urban eco-environment damage require special identification and evaluation systems. It is urgent to form a complete urban eco-environment damage assessment system.Based on an illegal occupation of a city in the suburban forest land, firstly, we completely and systematically analyzed the process of eco-environment damage identification and assessment, including acceptance of commission, preliminary investigation, project design, determination of time and space scope, baseline confirmation, causality analysis, damage confirmation, and the evaluation results being formed and adopted by the court, with the view to summarize the business process of eco-environment damage identification and assessment for urban ecosystem. In combination with the characteristics of the long duration of the destruction in this case (about 13 years) and the area of the involved forest land increased year by year (from the initial 6550m² to the final 24040 m²), the surrounding forest land that has not been damaged in the same period was used as "control plot". Through field investigation and related data analysis, this study determined the key parameters such as damage baseline of population density (2066 plants/hm²), stand height (6.4 m), biomass (104600 kg/hm²), etc. Finally, we calculated the eco-environment damage value to 2182573 yuan. The study of typical cases of eco-environment damage caused by occupation on forest land plays a leading role in highlighting the identification and evaluation of urban ecosystem damage cases.