It is very important in practice to avoid cascading failures by increasing the dynamic fault-tolerance of the network. Firstly, a cascading failure model is proposed in this paper, based on the characteristics of the variable load and the fixed capacity of the nodes in wireless sensor network scale-free topology. Then the influences of the load parameter and topology parameters on the fault tolerance are investigated in the case of cascading failure caused by random failure nodes. Finally the critical value of load for the large-scale cascading failure of network is deduced. Simulation result shows that the network's cascading failure fault-tolerance is positively related with the degree parameters, coefficient and power-law exponent. Researches provide regulation to avoid the cascading failure caused by the random failure nodes effectively from optimizing the parameters viewpoint.