By optimizing the pump structure, the axially non-uniform absorption coefficient of YAG crystal is compensated. A 15 mm diameter Nd∶YAG crystal is uniformly pumped. The effect of axially non-uniform absorption coefficient of Nd∶YAG on the uniform pumping is analyzed. Then a new method that can optimize the gain distribution through the modulation of the distance and the central pump wavelength is given. A side-pumped amplifier structure is designed to verify the simulation results by experiment. The scheme used for obtaining uniform gain distribution for Nd∶YAG rod with axially absorption coefficient with range of 2.343~2.882 cm-1 has been proved experimentally.