The utility model relates to an output mirror shared double-resonator-cavity Q-switched laser. Two paths of laser are generated in two different spatial light splitting manners, and then combined and output via a shared output mirror. In one light splitting manner, light is split in one optical path, a light beam passes through a second total reflective mirror with a small hole and is then split, one part in low-order mode passes a Q-switched device after passing through the small hole, and the other part in high-order mode is reflected, in the periphery of the small hole, back to a gain medium and output in an oscillation manner. In the other light splitting manner, light is split in two optical paths, the second total reflective mirror is included, two paths of light beams are generated via a light splitting device, one path provides power with high average, the other path generates power with high peak, and then the two paths are output via the shared output mirror. According to the utility model, split light is output via the shared mirror in different manners, power with high average and power with high peak can be simultaneously output, and light beams with high pulse energy and peak power can be simultaneously obtained; and the generated light beam includes the waveform in which a pulse peak is overlapped on a step in spatial distribution, the step reflects the average power, and the pulse peak reflects the peak power.