Abstract: The Nd:YAG slab end-pumped by laser diode arrays features small thermal effect and wavefront distortion. The theoretical analyses show that inhomogeneity of the temperature field and stress field is the main cause of wavefront distortion in the slab gain medium. For the end-pumped conduction cooled slab gain module, we optimized the pump and thermal uniformity by reasonable design and obtained the static wavefront distortion with a peak-valley (PV) value of 0.22 m. We tested the wavefront distortion of this module in the double-amplifier experiment device, deriving the PV values of 3.49 m without the signal power injection and 0.59 m after energy extraction. At the injection power of 3120 W, we obtained an output power of 4660 W and a beam quality value of 3.88 times the diffraction limit, with an optical-optical efficiency of 27%.