The government budget, as a national fiscal revenue and expenditure plan, specifies the scope and direction of government activities, including environmental governance, and is an important policy tool for enhancing the modernization of environmental governance capabilities. Giving full play to the guiding and governing role of the government budget in winning the battle against air and water pollution and soil contamination is of great significance to the continued modernization of the environmental governance system and governance capacity. Budget deviation is an important indicator of government budgetary capacity and influences local government environmental governance behavior. Analyzing from the perspective of budget deviation, this paper examined the integrated environmental governance effect of the government budget by constructing a fixed-effects model using data on budget deviation and industrial pollutant emissions in 291 prefectural-level cities in China from 2007 to 2020. The result indicated that: ① During the sample period, the government budget had an integrated environmental governance effect, which could significantly improve local environmental governance. ② Path analysis showed that the government budget could incentivize and constrain local environmental governance behavior. In terms of budgetary revenue deviation, the government budget could influence government environmental governance behavior through tax constraints that regulate local government fiscal rules. In terms of budgetary expenditure deviation, the government budget guided the direction of local government governance by increasing the share of environmental protection inputs, which in turn enhanced environmental governance. ③ Heterogeneity analysis showed that the integrated environmental governance effect of the government budget was affected by institutional factors and regional resource stock and structure, which was more pronounced in regions with weak environmental regulations, low environmental performance assessment, low pollution self-purification rate, and low administrative hierarchies. Based on this, this paper puts forward the following suggestions: developing a modern budgetary system to give full play to the functional role of the government budget in environmental governance; strengthening the incentive and constraint mechanism and continuously promoting integrated budget performance governance; strengthening budget supervision and harnessing the synergies of the national supervision system; and improving environmental regulations and environmental performance assessment systems, accelerating industrial transformation, and bringing into play the functional effect of the government budget in the field of environmental governance. This paper enriches the related research on government budget and environmental governance, which is conducive for the local government to formulating relevant policies according to local conditions, improving the role of the government budget in local environmental governance, and accelerating the modernization of the environmental governance system and governance capacity. [ABSTRACT FROM AUTHOR]