In electric power systems,both power generation and load have frequency response characteristic.As the operating status of power grid changes,the frequency response characteristics of the generator unit and the load fluctuate randomly.On the basis of the characteristic that the primary frequency modulation performance of the load and the power generation in electric power system is uncertain,and in connection with the concept of dynamic power flow,a probabilistic power flow calculation model considering the uncertainty of the static frequency characteristics of the generator unit and the load is established,and a method combining Monte Carlo sampling with cumulant is applied for analysis and calculation,in order to figure out the probabilistic distribution of active power flow of each line when a fault occurs in the system.IEEE-30 node system is taken as an example for calculation to analyze the impact of different responses of units on the power flow distribution of various branches.The method discussed herein is compared with the Monte Carlo simulation method to verify its effectiveness.