To reduce the thermal effect to beam quality in solid-state laser with high repetition rate, multimode optical fiber as phase conjugator has been experimentally investigated in an laser diode-pumped, electrooptical Q-switched Nd∶YAG laser with double-pass amplifier. The laser was operated on 100 Hz repetition rate and 20 ns pulse width. Perfect correction of laser profile distortion in amplifier and beam quality close to diffraction limit has been achieved. Pulse width of phase-conjugated laser was compressed to 7 ns while compression ratio reached 3∶1. Beam glitter has also been observed in lower pumping energy close to stimulated Brillouin scattering (SBS) threshold. With increase of energy coupled into fiber, that phenomenon was weakened, and higher stability was achieved. In the case of 5.3 mJ input energy, instability less than 14% is obtained, while SBS reflectivity and depolarization ratio were 32.6% and 7% respectively.