The invention discloses a method for calculating the fixed value of power flow protection of a multi-terminal flexible DC distribution network. The technical scheme of the invention comprises the following steps: establishing a mathematical model of a VSC: analyzing the loss type difference of a converter when the converter is used as a rectifier or an inverter according to the polynomial functionof the phase current of the converter through proper modeling of the converter loss; developing the power flow algorithm of the multi-terminal flexible DC distribution network: analyzing the influence of converter loss in the multi-terminal flexible DC distribution network on power flow solution when DG connection is carried out in proper position; establishing a multi-terminal flexible DC distribution network model: based on an IEEE33 bus in the distribution network, adding converters between different buses to analyze the influence of converter loss and network loss; and finally, verifyingthe feasibility and correctness of the multi-terminal flexible DC distribution network model by the simulation analysis of the topology structure in the multi-terminal flexible DC distribution system.The method realizes the protection of the DC distribution network.