Frontier researches have gradually noticed that governing performance on both economic development and environmental pollution can impact the political promotion of local officials in China. However, existing literature mainly explains the assessment mechanism in an isolated manner, which may fail to explain local officials' strong incentive to reduce pollutant emission when economic performance still held a prior position. Using the data of 810 observations of municipal party secretaries from 281 cities during 2005–2015, this paper examines the threshold effect of environmental pollution on the municipal party secretaries' economic promotion tournament. The results demonstrate that only when environmental pollution is below a certain level, can economic performance significantly increase local officials' promotion probability. Moreover, the significant threshold effect only exists for cities with stricter environmental governance and lower economic growth target. This research provides a deeper understanding of the special role of environmental performance in local officials' promotion assessment in China, which also has practical implications for countries struggling economy-environment trade-off to learn how to overcome this dilemma.