The present invention discloses a bilateral trade transmission loss allocation method based on a network splitting method, belonging to the network equivalence conversion technology field. The method comprises the following steps: 1) obtaining accurate transmission loss of each branch and the total transmission loss of the network according to an alternating current power flow calculation method; 2) determining the reserved branches of the converted network according to the network topology structure and the bilateral trade; 3) calculating and obtaining the power flow distribution of each group of the bilateral trade in each branch of the network according to the reserved branches; and 4) performing transmission loss allocation according to the proportion of the branch current flow caused by a single transaction in the total branch current flow caused by all the transactions. The bilateral trade transmission loss allocation method based on a network splitting method is configured to apply the network splitting method firstly to the transmission loss allocation and build a allocation cost model based on each transaction and perform solution so as to accurately reflect the power and the transmission distance of each transaction, solve the problem of the parallel flow and the counter-current flow in the cross-district transaction transmission loss allocation, and allow the transmission loss to be reasonably allocated to each transaction.