Abstract: A laser diode array (LDA) zigzag side-pumped polygonal thin-disk laser amplifier configuration was introduced. The three-dimensional ray tracing method was used for the detailed simulation, and the pump coupling structure of this amplifier system was optimized and designed. The effects of the doping ion concentration of polygonal gain medium and the side cutting angle on the pump light distribution in medium were mainly studied. Under the condition that the crystal thickness is 1.5 mm and the end face diameter is 16 mm, when the side cutting angle in the range of 35° to 65° and the Nd³⁺ doping concentration in the range of 0.20 at.% to 0.30 at.%, the Nd:YAG polygonal thin-disk has relatively uniform distribution of the pump light in simulation, and the pump light distribution uniformity is better than 0.1. The flat-topped distribution of fluorescence and gain distribution are also obtained in the experiment. The uniform flat-topped distribution of energy storage in medium is conducive to the realization of high power and high beam quality laser output, which provides many important references for the design and experiments of the zigzag side-pumped polygonal thin-disk laser system.