In view of the low measurement redundancy and frequent switch changes in distribution network, it is difficult to identify the correct topology. A topology identification method based on branch active power is proposed. Based on the residual value of active power, he method selects the branches that may be disconnected and obtains several possible topologies. The state estimation is carried out under each possible topology with the same measurement value, and the matching objective function value is calculated. The topology with the highest possibility is found from the set of possible topologies as the trusted topology. This method greatly reduces the solution space of distribution network topology analysis by calculating the branch active power residual value, and introduces the fast power flow direct current method to estimate the state, which improves the calculation efficiency of the algorithm, thus transforming this kind of distribution network topology error detection problem into a distribution network reconfiguration problem with high matching degree of measured values. The example shows that the method is reasonable, effective, fast and simple, and has good adaptability in the case of large measurement error.