The difference-in-differences model was used to examine the effects of implementing the "three red lines" policy on the debt structure of listed real estate firms. The empirical results indicate that a significant negative impact on current liabilities and a positive effect on long-term liabilities occur due to the "three red lines" policy, leading to an optimized adjustment of corporate debt structure. Further research finds the following. A more pronounced effect on the debt structure adjustment is observed in firms with a higher proportion of fixed assets than firms with a lower proportion. State-owned firms and real estate firms in non-eastern regions experience greater effects from the policy regarding their debt structure. Companies with weaker profitability and higher leverage are more significantly impacted by the policy, resulting in a more effective adjustment of their debt structure. The introduction of the policy accelerates the circulation of working capital in real estate enterprises and promotes the targeted use of long-term debt to replace short-term debt. A causal relationship between the "three red lines" policy and real estate enterprises is identified within the context of the "houses for living and not for investment" policy, elucidating the mechanism of the "three red lines" policy and providing important reference significance for market participants and the improvement of corporate financialization phenomena.