The innovation and development of the new energy industry is crucial to guaranteeing China's energy security, promoting high-quality economic development and alleviating the global climate crisis. New Energy Demonstration City Policy (NEDC) is one of the important policies to promote the development of the new energy industry in China. Academic research on their green innovation effect on new energy enterprises and the explanation of their influence mechanism still needs to be deepened. This paper utilizes panel data from listed companies in China spanning from 2011 to 2019 and employs the triple difference method to empirically investigate the impact of NEDC on the green innovation of new energy enterprises. Findings of the study are as follows: (1) The implementation of NEDC significantly promotes green innovation among new energy enterprises, a conclusion that holds true under a series of robustness tests; (2) Further analysis suggests that, from the perspective of patent heterogeneity, the "incremental" manifestation of this policy effect is more pronounced; (3) From the perspective of ownership heterogeneity, distinct from state-owned enterprises, the promotion of green innovation among private new energy enterprises is notably significant under the policy; (4) Mechanism analysis reveals that NEDC can alter the ways in which new energy enterprises acquire and utilize funds, thereby increasing R&D investment and facilitating green innovation. The research conclusions of this paper bear certain policy implications, providing theoretical foundations and empirical references for government departments to optimize and promote NEDC.