Dynamic impacts of multi-tier capital-market tax incentive mechanisms on SME financing efficiency

With the deepening of the global economic transformation and upgrading and the innovation-driven development strategy, the financing efficiency of SMEs, as an important carrier of economic vitality, is directly related to the sustainable development of the real economy. However, due to structural barriers such as information asymmetry, credit constraints and capital market access thresholds, SMEs have long faced difficulties in financing and expensive financing. To alleviate this problem, countries have successively constructed a multi-level capital market system by building differentiated platforms such as the Main Board, the Growth Enterprise Market (GEM) and the New Third Board (NSSB), and introducing incentives such as tax breaks and financial subsidies in order to optimize the allocation of resources and enhance the inclusiveness of the market. This study integrates reinforcement learning and causal inference methods to construct a framework for assessing the dynamic impact of multilevel tax incentives on SME financing efficiency, and employs the Markov decision process and double robust estimators to identify the evolutionary patterns of the policy effects in the time and structural dimensions. It is found that SMEs' financing costs are reduced after the implementation of tax incentives, and the policy effect responds most significantly in the emerging market segment. Heterogeneity analysis reveals that the intensity of policy response is significantly higher in the eastern coastal region than in the central and western regions, and technology-intensive industries benefit more. The results of the study provide important empirical evidence for precise incentive policy design, emphasize the necessity of tiered policy implementation and contextual matching, and have important theoretical value and practical guidance for maximizing the efficiency of fiscal policy and promoting financing equity.