The effect of pump homogenization on the beam quality of the output laser is studied for a compact partially end-pumped hybrid-cavity slab laser amplifier, i.e. Innoslab laser amplifier. Using ZEMAX simulation software, two pump coupling modes, direct imaging and homogenization with waveguide were designed, and their effects on the uniformity of light intensity distribution in the slow axis (crystal width) direction of laser diode arrays were compared. It is found that the pump uniformity is significantly improved after the waveguide is homogenized and the influence of the laser diode array luminescence dead pixels on the pump imaging is weakened. Furthermore, the effect of pumping homogenization on the performance of Innoslab laser amplifier is verified by experiments: the uniformity of slow-axis pumping increases from 90.6% to 95.4% after homogenization with waveguide, and the quality of output laser beam M² increases from 2.41 to 1.55 after three-pass amplification, and the self-oscillation in the cavity is effectively suppressed.