Multi-port converters with grid-forming control can achieve transient support for weak low-voltage distribution network. However, it has the risk that node voltages in distribution stations exceed the limit due to providing excessive active power. To mitigate the risk, a multi-ports converter power flow optimization control strategy based on active power proportion coefficient is proposed. Firstly, sensitivity matrix is used as the model of distribution station and parameters of the sensitivity matrix are updated with online measured data. Subsequently, for keeping the node voltages in distribution stations in safe range, the maximum active power output of each station is calculated based on the node voltage limit and the sensitivity matrix. Next, in order to ensure that the node voltage has the same proportional margin when providing transient support active power for each distribution station, the proportional coefficients of active power provided by each distribution station are set as the optimization objective. Finally, cases of weak low-voltage distribution network with or without supporting of multi-port converter are studied and the effectiveness of the proposed control strategy is verified through simulation.