The invention relates to the technical field of electrical engineering. The invention discloses a decision-making method and system for thermal power plant dispatching under a haze condition. Effective analysis of haze is achieved and powerful and rational basis is provided for decision making of dispatching of the heat engine plant. The method comprises the steps that historical environment monitoring data of a thermal power plant in a to-be-analyzed area are collected to obtain an initial data set, and the initial data set is divided into a training data set and a verification data set; Establishing a binary tree calculation model according to the training data set, and verifying whether the binary tree calculation model is valid or not by adopting a verification data set; And collectingenvironmental monitoring prediction data of the to-be-analyzed region at a future moment under the haze condition, inputting the environmental monitoring prediction data into the binary tree calculation model, and judging whether shutdown should be carried out or not according to an output result of the binary tree calculation model.