Rapid urbanization and climate change have converged to expose high-density cities to multiple ecological risks, including the urban heat island effect, flooding, and air pollution, which jeopardize the stability of urban ecosystems and threaten human well-being. Consequently, it is imperative to investigate ecological challenges and coping strategies in high-density cities worldwide. Uilizing Web of Science and Scopus as the data sources for literature search, 258 documents were systematically analyzed to elucidate the research characteristics of ecological issues within global high-density cities. Firstly, we analyzed the quantitative distribution and geographical characteristics of the ecological problems in these cities. Secondly, we deliberated on the influencing factors and scale differences associated with three principal ecological challenges as well as coping strategies at both urban and site scales. Lastly, it was indicated that, in the future, three-dimensional urban morphology and vertical greening will be focal points for addressing ecological issues. It can be concluded that: (1) Asia is the region most concerned with high-density ecological challeges, and the urban heat island effect is prevalent in all of high-density cities worldwide; (2) Landscape patterns and built environment characteristics are critical influences on the urban heat island effect and flooding, while biophysical characteristics and built environment characteristics are significantly impact on air pollution; (3) Optimizing the composition and configurations of urban landscapes can mitigate ecological problems associated with high desity. The findings of this study provide vital insights for ecological research and risk management in high-density urban areas.