Because the power system has many uncertainties, the deterministic method can not evaluate the risk of the shaft of the generator suffer from the transient amplification accurately, this paper presents a risk evaluation method. It takes the influence of fault clearing time on the transient torque into account, and introduces probabilistic collocation method to solve the probability density function of the transient torque. Meanwhile, it also defines the severity function of the transient torque amplification. On this basis, it determines the study area of the shaft of generators suffer from damage, reduces the scope of risk assessment, and thus more comprehensive and accurate risk assessment results is obtained. Finally, The results of calculation example of typical IEEE 16-machine 68-bus system show that the proposed assessment strategy is effective and practical.