Abstract: A mathematical parameter δ is adopted to assess the different space distribution in two laser fields. The effect of the pumping light space distribution on the quality of the ground-mode oscillating beam is analyzed by applying δ in the resonant cavity. The analysis for the effect shows that the ground-mode oscillating beam will drift off the Gauss distribution if the nonequilibrium gain distribution is caused by pumping light in the laser medium. With the parameterδ, the quantitative estimation was carried out for the effect of the pump light on the quality of oscillating beam. The investigation shows that the parameterδ, can directly represent the effect of pumping light distribution on the beam quality of laser, and the value of the parameterδ can be used to judge the pumping light distribution quality. As for the endpumping DPL with continuous operation, the most ideal distribution mode of the pumping light is the Gauss pumping light and its diameter is equal to that of the fundamentalmode Gauss oscillating beam of the resonant cavity.