The same-stage bidding of regional market entities can promote the optimal allocation of resources in the southern region and promote the construction and development of a unified market in the southern region. Interregional and interprovincial transmission prices are important parts of the price mechanism for the same-stage bidding and trading. How to set the prices is related to the interest distribution of the various market entities in the region. In view of the problems existing in the current transmission price mechanism, referring to the foreign transmission price mechanism of cross-regional transaction, a transmission price mechanism suitable for the same-stage transaction is proposed, and the transmission pricing method is clarified. The feasibility of the design mechanism in the same-stage bidding and trading is verified through comparative analysis.