The invention relates to a power grid topology error identification method based on the branch active power flow. The method includes following steps: reading a power grid model and measuring a section; generating a node branch model; merging a part of switches to a switch group; setting active power flow state quantities of the switches and the switch group; building a branch active power flow estimation model; and performing estimation by employing the weighted least absolute value or solving the estimation value by employing the weighted least squares. By adopting the method, the states of switch-on and switch-off of a switch are respectively estimated by employing the active power flow, the precision is high, and topology errors due to measurement error are effectively avoided.