In recent years, the direct-liquid-cooled thin-disk lasers have become ahot research topic due to their advantages of extremely small volume to output power ratio and strong thermal management ability. A method of analyzing the wavefront aberration of the direct-liquid-cooled thin-disk laser is established in this paper. The influence of pumping light uniformity on the wavefront aberration is investigated by this method. The high order aberration distribution of the laser beam is calculated, when the uniformity is 92%, 80% and 70%, respectively. With the decrease of beam uniformity, the higher order aberrationsincrease gradually, while the low order aberrations remain basically unchanged. Experimentally, the pumping beam distributions respectively with uniformity of 92% and 70% are designed with and without using the waveguide structure. The wavefront jitter and wavefront aberration distribution of the whole gain module are measured in these two cases. The pump power is kept at 5 kW. The higher order of optical path difference (OPD _H) values of the whole gain module are measured to be 0.66 μm and 0.79 μm, respectively. The experimental results are in agreement with the theoretical analyses.