With the increasing level of power line voltage and the use of large-capacity units

the frequency dynamic process and spatial distribution characteristics will be more significant under large-scale power loss. Frequency analysis by the power flow method is mainly limited by power system scale. Based on the analysis of existing frequency dynamic models

a newmethod of fast response analysis（FRM） based on reduced admittance matrix is proposed. This method simplifies the system admittance matrix by eliminating the load nodes

and uses the simplified admittance matrix to directly compute the power oscillation process between units and dynamic change process of frequency. Simulation results of two test systems show that the FRM can reflect the influences of the units distribution feature on frequency and the relationship between the active power and frequency effectively. The calculation speed of FRM achieves ten times faster under the same calculation accuracy. It can be used for long-time frequency analysis in large-scale power system.