Abstract: Based on the cross-regional electricity trading,electrical regime and price polices in China,transmission reliability indices are constructed,and a unified cross-regional transmission pricing model considering reliability is presented.The model consists of two layers.Firstly,it proposes calculation methods of long-run marginal cost of transmission reliability through deep analysis of the electricity transmission cost,and a user transmission pricing model is built considering reliability based on the grid using extent and long-run marginal cost of transmission reliability.Secondly,a transmission revenue distribution model is constructed considering investment of transmission lines and its reliability contribution,and an economic incentive model of fine fund is established and induced for excessive transmission investment.With the selection of the unified pricing mechanism,the model overcomes the shortcomings of the multi-level overlay pricing method（MLO）and the point of connection tariff（POC）which cannot clearly reflect the insufficient use of the power grid by the transmission devices of cross-regional transactions.And the model is fairer,simpler and more transparent to settle accounts.By introducing reliability component,it is able to provide economic signals of transmission congestion and to effectively guide transmission investment.Results of IEEE57-bus test system illustrate its rationality and effectiveness.