Abstract: Cascading failures are the main cause of power grid blackouts, and the large-scale grid-connected renewable energy resources further increase the risk of power system cascading failure. In this paper, an improved probabilistic load flow method considering wind power uncertainty and system frequency modulation was proposed and applied to the event chains search and risk assessment of power grid cascading failure. Firstly, the probabilistic load flow calculation method considering the effect of system frequency modulation was derived on the basis of the conventional probabilistic load flow, and the observation of system frequency was added to the output state variables. Secondly, regarding the overload fault on the transmission line, the outage probability model of the next level overload line fault was established combining the line power probability density and the line outage function. Furthermore, the frequency confidence was introduced to implement the configuration of over-frequency generator tripping and under-frequency load shedding stability control measures during the event chains search process. Finally, the simulations and comparative analysis were conducted on the IEEE 39-bus system and the IEEE 118-bus system to verify the rationality and validity of the proposed model and method.