There are typically uncertain parameters in power system models， and it is consequently impacted that the credible degree of dynamic behaviors of power system simulations relied upon these uncertain models. Based on optimal power flow constrained by transient stability， this paper presents a computational method for evaluating the credible degree of dynamic behaviors of simulations in the condition of parameter uncertainty. In the method， a set of nonlinear optimization problems is formulated to determine dynamic performance bounds around nominal values. The performance bounds are the basis of evaluating the credible degree of dynamics of simulations in the condition of uncertainty. These nonlinear optimization problems are solved by a successive linear programming approach. The proposed method is tested on the IEEE 9-bus test system and the IEEE 39-bus test system. The results show that the proposed method is effective in evaluating the credible degree of dynamic behaviors of power system simulations in the condition of parameter uncertainty.