For the advantage of long-life, high efficiency, low heat load and compact structure, diode pumped Laser (DPL) is used widely in different field such as military, communication and medicine etc. Diode-pumped Nd:YAG laser module is the integration of diodes (pumping source), coupling structure, cooling structure and laser medium through optimization. Being the core component of diode-pumped MOPA laser, the gain distribution of diode-pumped amplifier module influences the beam quality greatly. So it is very important to improve the uniformity of the module with high pumping power. This paper investigates, theoretically and experimentally, the elements which influence the gain distribute of laser medium. A high energy storage laser module have been manufactured. In this module a 8mm diameter Nd:YAG rod which is 120mm long is pumped by twelve diodes-arrays (the peak pump-power is 12kw). Each array is consisted of twelve diodes. Numerical calculation has been done to optimize the coupling structure. The experiment result approved that the gain coefficient of this module is 0.186/cm, from it we can infer that the storage power is about 700mJ per pulse.