This article proposes a rotordynamic identification method using the accelerating sweep frequency excitation method. The computational fluid dynamics transient solution combined with the moving grid method is utilized to obtain the transient flow field of the seal excited by the whirling rotor with an accelerating frequency. Rotordynamic coefficients at swept frequencies are obtained by analyzing the transient response force acting on the rotor. Rotordynamic coefficients of three published experimental seals including a labyrinth seal, a fully partitioned pocket damper seal and a honeycomb seal are identified to validate the proposed method. The results show that the predicted rotordynamic coefficients are all well agreement with the trend of experimental data. Compared with the existing numerical models based on transient solutions, the central processing unit consumption of the proposed method is substantially reduced by 98% when achieving the same frequency resolution. In addition, the impact of the exciting acceleration on the identification accuracy is also illustrated.