To obtain the actual bandwidth and RC time constant of the passive integrator, the frequency characteristics of the integrator under 1 MΩ load are measured by using an active high impedance probe and a network analyzer. The simulation results show that the low frequency inflection point of integrator with 1 MΩ load is much lower than that of integrator with 50 Ω load, and the measured results are consistent with the simulation results. The measured results show that the high frequency band of the integrator frequency characteristic deviates from the theoretical trend of linear attenuation inversely proportional to the frequency, which is related to the spurious parameters of the actual circuit. The upper frequency limit of the integrator is determined by transforming the ordinate, and the working bandwidth of the integrator can be obtained by combining the calculated low frequency results. The RC constant is calculated by using the amplitude-frequency characteristic formula of integrator combined with the frequency sweep measurement results, which is simple and has less uncertainty.