The power flow calculation is a significant basis for the optimized operation of integrated energy systems. For two-way coupled electricity–gas integrated energy systems, the dynamic characteristics of the slow time scale of the gas subsystem make the steady-state energy flow calculation unable to accurately obtain its real-time operating status. In this paper, for the electricity–gas integrated energy system, propose a time-domain continuous power flow calculation method considering the dynamic process of the gas subsystem, which can obtain continuous change of the state variables. The Taylor series expansion method is applied to the power subsystem, the unified energy path model and matching calculation method is used in the natural gas subsystem. The solution is realized by alternating the input and output variables of the coupling element. At the same time, the input of the power subsystem derivative information and the natural gas subsystems frequency domain information makes this method obtain continuous solutions in the time domain, which can meet the time scale requirements in different scenarios. Finally, a calculation example is carried out, and the results show that compared with traditional discrete method, this method can greatly reduce the calculation time under the condition of ensuring a certain degree of accuracy, which verifies the effectiveness of the proposed method.