With the advancement of electricity market reforms, the rapid development of intra-provincial and inter-provincial electricity transactions has placed higher demands on transmission section planning. Traditional models often overlook the complexity of market gaming behavior, making it difficult to accurately reflect the economic value of transmission investments. In response, a method for evaluating the value of transmission sections is proposed, considering both intra-provincial and inter-provincial electricity spot market transactions.By constructing an inter-provincial equilibrium constraint model and an intra-provincial centralized clearing model, the method comprehensively accounts for market clearing rules and price signals to assess the market value of transmission expansion. A case study based on the Jiangsu power grid topology shows that insufficient inter-provincial transmission capacity can lead to increased price volatility and market failures. Transmission expansion effectively mitigates these issues and promotes rational bidding, while the evaluation of intra-provincial sections demonstrates that market value indicators can significantly enhance resource allocation efficiency. Adjusting the expansion revenue distribution coefficient and investment ratio can further optimize grid companies’investment decisions across different energy structures.