Abstract: For a high power superconducting proton linac, the transient beam loading effect is an important factor affecting the amplitude and phase stability of the electromagnetic field in a superconducting cavity. Based on the resonant cavity field model, a time-domain simulation code for the beam loading effect in a superconducting cavity was developed, and the simulation results were verified in the prototype injector II of C-ADS. It was then evaluated the influence of pulse width, feedforward timing jitter and beam ripple for CiADS. The simulation results, to meet the design specification, showed that the Radio frequency(RF) fluctuations for each cavity should be less than 0.1% in amplitude and 0.1^\circ in phase. And the feedforward timing jitter should not exceed 0.79 µs, the beam DC deviation should not exceed 0.9%. The relationship between the maximum ripple amplitude and the ripple frequency was given. These results will provide a basis for determining technical specifications of relevant sub-systems of CiADS.