This paper theoretically and experimentally investigated the elements which influence the gain distribution of laser medium. A high energy storage laser module was manufactured. In this module an 8 mm diameter Nd:YAG rod which was 120 mm long was pumped by twelve diodes-arrays (the peak pump-power was 12 kW). Each array consisted of twelve diodes. Numerical calculation was done to optimize the coupling structure. In order to satisfy the condition of reducing heat, a microchannel cooling structure was adopted. The experiment result shows that the gain coefficient of this module is 0.186/cm and the storage power is about 700 mJ per pulse.