The ray tracing and Monte Carlo method are applied to calculate the distribution of deposited pumping energy within a rod amplifier of the high power solid state laser system. Allowances are made for the effects of multiple reflections on the reflector and laser rod, Xe flashlamp emission spectrum and absorption spectrum of Nd doped laser glass. The results obtained are good agreement with the experimental results of gain uniformity measured by threshold method and laser wavefront measured by Hartmann wavefront sensor.