In this Letter, a high-power diode-side-pumped Nd:YAG laser emitting at $1338\mathrm{nm}$ is described. The output characteristics of the laser using the different output couplers for both the cw mode and the Q-switched mode have been studied. With a pumping power of $555\mathrm{W}$ , the average output power decreases from $70\mathrm{W}$ at $50\mathrm{kHz}\text{to}55\mathrm{W}$ (slope efficiency 21.2%, optical conversion efficiency 10%) at $5\mathrm{kHz}$ . The highest peak power is up to $73\mathrm{kW}$ with the pulse duration of $150\mathrm{ns}$ at the repetition rate of $5\mathrm{kHz}$ . When operated in cw mode, the output power of $100.5\mathrm{W}$ was achieved, corresponding with the optical slope efficiency of 36%.