The invention relates to a transmission grid loss allocation method in hybrid transaction mode. The transmission grid loss allocation method in hybrid transaction mode includes the steps: respectively acquiring the power flow distribution of bilateral transaction and joint transaction in the network structure for hybrid transaction; and respectively determining the allocated transmission grid loss of the bilateral transaction and joint transaction in the network structure for hybrid transaction. The transmission grid loss allocation method in hybrid transaction mode takes joint transaction as one transaction and takes a direct current power flow as a hypothetical premise, performs allocation of the accurately calculated alternating current transmission grid loss according to the proportion of each transaction on each branch of power flow, and is suitable for the bilateral transaction and joint transaction hybrid transaction mode.