Rayleigh scattering-stimulated Brillouin scattering (RS-SBS) passive Q switched Er-doped fiber (EDF) laser has the potential to achieve low repetition, short pulse duration and high peak power, which satisfy the requirement for the optical pulse source of optical time domain reflection (OTDR) system, but the repetition frequency is not stable enough for real application. So, a hybrid Q-switched Er-doped fiber laser by inserting an acousto-optic modulator (AOM) into the RS-SBS passive Q cavity was proposed and studied. For the pump level of 120～200 mW, the repetition frequency of the output pulse strain can be continuously adjusted from 30 Hz to 90 kHz. The peak power can be about 200 W and the pulse duration can be about 20 ns. The stability of the repetition frequency is better than 5% and the amplitude fluctuation is less than 10%. The peak power and pulse duration are almost independent on the pump level, but the peak power will reduce and the pulse duration will increase as the modulation frequency increases.