This paper summarizes the results of simulation of a module for side-pumping a Nd:YAG rod. The module consists of three laser diode arrays separated by 120° rotation angle around the laser rod, where each array contains 10 emitters producing a maximum output power of 15 W at 808 nm wavelength. This high power diode pumped solid-state (DPSS) laser system was modeled in both LASCAD and GLAD simulators. LASCAD model was used to simulate the laser output power as a function of the total input power and the output mirror reflectivity. The model predicted an output power of 140 W given 400 W total input pump power with optical efficiency of 35%, in a good agreement with the published experimental results and similar commercially available CW DPSS laser systems. LASCAD was also used to model the temperature distribution inside the rod and to examine the heat load and thermally induced mechanical stress on the rod. Simulation in GLAD enabled a detailed analysis of the beam quality, beam size, and mode stability inside the resonator. GLAD models were used to simulate the pumping light distribution in the Nd:YAG rod for a single diode element, a single diode array, and three diode arrays. The GLAD shows that a stable multi-transverse mode "top hat" beam is formed after 30 passes through the resonator of the adopted high power DPSS laser system.