To ensure that the frequency is within a reasonable range is basic requirement for safe and stable operation of power grid. In current time-domain simulation analysis methods of transient frequency stability of power system, most of frequency related parameters of transmission lines are fixed as rated values. With the increasing proportion of new energy sources, the frequency dynamic process analysis of new power systems is no longer limited to generator nodes, and the differences of inertia, frequency spatio-temporal and frequency modulation resource distribution are more significant. The frequency of each node is obviously offset under large disturbance, and the accuracy of frequency analysis results obtained by traditional numerical differentiation is difficult to guarantee, which is difficult to reproduce the actual frequency change track after the occurrence of power network faults, affecting the accuracy of frequency analysis and control. Therefore, a new transient frequency analysis method based on frequency divider theory is proposed in this paper. Compared with traditional method, The method can accurately simulate transient conditions in the transient process, and the node frequency varies with electrical distance between nodes, transmission line and transformer reactance, which can accurately simulate transient conditions and dynamically modify the element frequency parameters in the model, characterizing the frequency characteristics of system after disturbance more accurately and improving the accuracy of the time domain simulation and analysis more effectively. The correctness and superiority of proposed method are verified by simulation, which can provide a new idea and reference scheme for frequency analysis and control design of new power system.