This paper explored the main driving forces and stresses contributing to the eco-environmental changes of Baishan City in Jilin Province, through the analysis of the ecological security problems in the City. The framework of DPSIR was applied to establish an ecological security assessment index system, and further, to create an ecological security assessment model suitable for mountain areas. By using the 1989, 1999, and 2006 TM images, and in combining with the DEM data and field survey data, the interpretation of the land cover in Baishan City was conducted, and the landscape classification was carried out. With the support of Fragstats, the important ecological indicators were extracted. Then, the situations of ecological security in various districts and counties of Baishan City were assessed. The results indicated that there was an obvious regional difference in the ecological security of Baishan City, with a deteriorating trend of the overall ecological security situation. Human activities had deeper influence on the land cover pattern and species habitat distribution, and even, became the main driving force of the pattern changes in ecological security.