A novel Er:YAG laser system operating at 1645 nm with high pulse-repetition-frequency (PRF) of kHz level is demonstrated. A ring cavity with double gain medium end-pumped by two fiber lasers is utilized to obtain high pulse energy. A novel ‘triple-reflection’ configuration on a piezoelectric actuator (PZT) is adopted to achieve high-repetition-rate at 3-kHz operation with the ramp-fire locking method. Single frequency pulses with maximum average power of 18.3 W at 3 kHz are obtained, and the pulse duration time is 318 ns. The full line width at half maximum (FWHM) of the pulses measured by the heterodyne technique is 1.71 MHz at 3 kHz. To the best of our knowledge, this is the highest PRF single-frequency laser pulses achieved based Er:YAG gain medium.