The influence of inlet pressure fluctuation on performance of disk CCMHD generator is examined with γ-θ two dimensional numerical simulations. It is confirmed from the simulation concerned with the behavior of the impulsive pressure disturbance that Magneto-acoustic waves exist even under the condition of fully seed ionization in γ-θ two-dimensional plane. Small continuous inlet pressure fluctuations about 1% are found to reduce the output power hardly. The large fluctuation about 10% can cause the ionization instability and result in the slight reduction of the performance.