Multi-energy flow means multiple types of energy flow, including mutual coupling, conversion and transmission of energy flows, such as cold, heat, electricity, gas and other energy forms. Among them, the electrothermal coupled multi-energy flow system represented by electric heating and co-generation has developed most rapidly, bringing many benefits and making safety problems more prominent. In this paper, the calculation method of electro-thermal multi-energy flow system is proposed considering safety factors. Firstly, the thermal network, power network model and coupling component model are established. Then, the expected fault set is constructed based on security factors. The distributed sequential power flow algorithm is used to solve the problem. The two grids and islands are analyzed. Finally, the actual example is passed. The superiority of the proposed algorithm is verified.