High-repetition-frequency Q-switched laser is realized through adopting a Nd:LaMgAl11O19 (Nd:LMA) disordered crystal as the gain material, a laser diode lasing at 796 nm as the pumped source, and a semiconductor saturable absorber mirror (SESAM) as the Q-switched device. The out-put characteristics are analyzed under using different transmittance T plane mirrors as an output coupler. Without adopting SESAM, the laser is operating at a CW state, and a relatively high transmittance is helpful for achieving high output power, slope efficiency and light-to-light efficiency. ForT = 7.5% and an absorbed power of 6.17 W, the output power arrives at its maximum of 1160 mW,and the corresponding slope efficiency and light-to-light efficiency are 20.71% and 18.78%, respectively. After introducing SESAM into the cavity, the laser operates at a passively Q-switched state, and the largest slope efficiency is 13.14% under T = 5.0%. Adopting five different output couplers, with the increase of the absorbed power, the pulse repetition frequencies, the pulse energies and the peak powers will ascend while the pulse widths will decline. The observed narrowest pulse width, the maximum pulse repetition frequency, the highest pulse energy and peak power are 1.745 μs, 175.88 kHz, 3.21 μJ and 1.84 W, respectively.