A high-beam-quality and high-stabil ity laser amplifier based on LDA side-pumping Nd-glass applied to amplify a na nosecond laser pulse source has been developed in this paper.The main technique of the laser amplifier is the multilevel double-pass amplification and liquid crystal spatial light modulator (LCSLM) in near field control.The beam quality i s one of the standards that measure the laser′s quality;its high quality can im prove the working flux and load capacity of the device,which plays a positive pa rt in reducing the risk of damage for optical elements as well.The LCSLM is used in the amplifier for spatial beam shaping so as to improve the near-field unif ormity,and compensating for real-time and adjustable laser beam by LCSLM can ef fectively control the near-field beam modulation.When the flat top pulse with t he width of 3ns and energy of 500nJ is injected as the seed pulse,the average output energy of the laser amplifier is 100mJ.The modulation degree of near fie ld is less than 1.22∶1,the energy dispersion degree of the output laser is 2.14%,and the beam angle drifting of the far-field is less than 11μrad.