<p>With the rapid urbanization process, as a reaction to the negative impacts of economic development on society and environment, sustainable development has become a consistent aim for all the countries in the world. Sustainability assessment is an important approach to promote the sustainable development of cities. Liaoning, as a traditional raw material and heavy industry base in China, has developed some associated policies to realize its sustainable development. This paper aims to assess the sustainability of the cities in Liaoning province by selecting 18 indicators from three dimensions: economy, environment and society. A deviation maximized decision making trial and evaluation laboratory (DM-DEMATEL) weighting method was proposed to calculate the indicator weights. This method not only amplifies differences among alternatives but also incorporates intrinsic indicator significance, thereby enhancing the comprehensiveness of sustainability assessments. Moreover, the regional sustainability differences of the 14 cities were analyzed with the measurement of the Gini index. The assessment results indicate that the sustainable development of the cities in Liaoning province were not optimistic, only 5 cities had positive sustainability performances in the years 2011–2020. But we find that the cities such as Shenyang, Panjin and Huludao had positive sustainability growth rates and showed a better development momentum. Furthermore, the regional sustainability in Liaoning province showed significant differences, and the differences presented a widening trend. Sustainability in southern and northern Liaoning was considerably better than that in western and eastern Liaoning. The research findings provide valuable insights for policy makers to formulate targeted policies and initiatives, which are helpful for optimizing resource allocation, boosting industrial competitiveness, and ultimately promoting the construction of sustainable cities in Liaoning province. </p>