Abstract: To explore the collusion and loan fraud behavior of low-carbon supply chain enterprises with financial constraints in the context of green finance, a tripartite game model is constructed among banks, core enterprises, and small and medium-sized enterprises. The model identifies the key factors that drive collusion between core enterprises and small and medium-sized enterprises to defraud green loans from banks in low-carbon supply chains. Also, the impact of bank regulatory cost, regulatory success rates, and collusion penalty levels on enterprise collusion decisions and bank regulatory strategies is analyzed. Results show that the “operational ease” and “concealment” of collusion among enterprises, as well as the regulatory cost and penalty levels of banks, are key factors influencing collusion behavior in low-carbon supply chains. With the continuous increase in bank regulatory cost, its motivation and intensity are weakening, leading to a high probability of enterprise collusion. When the green lending rate of a bank is relatively high, that is, when its gap with the ordinary lending rate is small, the probability of collusion among enterprises increases. By investing in and deploying emerging technologies to enhance regulatory efficiency (i.e., higher regulatory success rates) and by strengthening penalties for collusion, banks can effectively deter such behavior and reduce both the motivation and probability of collusion.