The output laser beam from a pulsed diodes side pumped single longitudinal mode laser is amplified by single passing through two pre-amplifiers and two main amplifiers, by which single longitudinal mode laser with pulse energy of 36.5 mJ, pulse width of 24 ns at 400 Hz repetition rate is obtained, with beam quality factor being M2x=1.78, M2y=2.13. After applying a large aperture tapered fused silica fiber as phase conjugating mirror, which shows more than 50% stimulated Brillouin scattering reflectivity, the input laser pulse width can be reduced to 6 ns and peak power increased significantly. The returned laser backtracks because of the phase conjugation characteristics and passes through two main amplifiers again, not only compensating the phase aberration of the laser amplifier crystal but also distilling more energy and amplifying the laser effectively. Finally, single longitudinal mode laser with pulse energy of 101.25 mJ, pulse width of 6 ns at 400 Hz repetition rate is achieved, corresponding to a peak power of 16.8 MW. Its beam quality factor is M2x=1.74, M2y=1.93. Obviously, the beam quality is improved instead of deteriorated after applying the phase conjugation mirror. However, the beam quality deteriorates to M2≈4 by using plane high reflective (HR) mirror, which validates the effectiveness of the phase conjugation mirror.