The ecological security evaluation of a coal resource-based city can help manage the imbalance between a population, resources, and the environment, so as to ensure sustainable development of the city. The entropy weight TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) model was used to evaluate the ecological security of Xilinhot, a coal resource-based city; an obstacle factor of the city was then diagnosed through an obstacle degree model. The entropy weight TOPSIS method helps fully utilize original data, enabling a comprehensive assessment of the ecological security of an urban ecosystem, revealing each indicator level as well as the key factors affecting a system. An eco-security evaluation index system involving 33 indexes was established under a PSR (Press-State-Response) model based on aspects of ecological environment and social economy. The results showed that: (1) The development of ecological security levels in Xilinhot city, as a whole, increased gradually from 2008 to 2017. The safety level changed from less safe to critical as the index increased from 0.464 to 0.553; (2) The three PSR indices showed different characteristics in the last 10 years. The pressure index trend demonstrated an increase, following a decrease; decreasing slightly thereafter. The state index increased in a fluctuating manner, and the response index demonstrated rapid growth; (3) The subsystem obstacle degree indicated that the pressure system was the primary factor affecting the ecological security of the coal resource-based city. The obstacle degree of the pressure and state system increased by an annual average of 6.04% and 2.11%, respectively, but that of the response system decreased by 11.15%; (4) Considering the index layer, the main factors affecting ecological security are attributed to the pressure and state systems. In 2008-2012, the obstacle degree of urbanization rate was maximum; in 2013-2017, the first obstacle factors changed, and mineral area became the major obstacle factor.