The DC power distribution network is a development trend of the future intelligent power distribution network because it can flexibly accept distributed power and DC loads. With the increasing of the load demand in the DC distribution network, the system would collapse due to the static voltage instability. Therefore, it is very important to study the load margin of the DC distribution network to ensure the safe and reliable operation of the system. In this paper, the power flow model of DC distribution network is established firstly, and the power flow model with the dual active bridge DC-DC converter is embedded in the power flow model of DC distribution network, and the load margin calculation method of DC distribution network based on continuation power flow method is proposed. Through the simulation of two typical topologies of DC distribution network, the results show that the DC distribution network optimizes the AC distribution network in terms of reducing the network loss and improving the power supply capacity, and the increase of DC-DC converter ratio helps to improve the load margin.