The development model of "capital investment, resource trumpet, and pollution-intensive" violates the laws of economy and nature, and gradually reaches the limit of economic growth. The pollution and environmental damage caused by it has become the main limiting factor for the sustainable development of urban economy and society. Actively developing circular economy, taking into account economic development, resource conservation and environmental protection, and coordinating economic, social and environmental development is a necessary opportunity for urban economic development and an important way to build a green city. The circular economy is a systemic project linking the economy, technology and society. It cannot be implemented and promoted without the political support of the government, and fiscal policy is an ideal policy tool. Therefore, a comprehensive assessment of the role of fiscal and economic leverage is required, and fiscal policies that actively support the development of a circular economy need to be improved. Through the research and experiment of digital finance to promote the development of circular economy in a sustainable environment, this paper has shown that: in 2015, the general public budget expenditure of Lanzhou Municipal Government increased from 28.219 billion yuan in 2014 to 34.9 billion yuan, an increase of 6.681 billion yuan, the growth rate also increased from 16.61% in 2014 to 23.85%. Among them, the government's expenditure on energy conservation and environmental protection has also increased from 1.068 billion yuan in 2014 to 1.632 billion yuan. It can be seen from the above data that the support of digital finance has a significant effect on promoting the development of circular economy in a sustainable environment.