Effect of the pump light on the quality of diode pumped laser (DPL) has been di scussed. Based on the end pump system, the equation of the laser field has been studied, which shows that the distribution of the laser gain can affect the la ser mode and make the base mode of the laser to drift off from the Gauss distrib ution . A factor is proposed to estimate the scale of the affection, which is called a f fection factor of pump light. Calculations on the end pump laser prove that the factor is practical and convenient. Study on the Qswitched laser show that the field distribution of the pulse is also affected by the distribution of the pump beam. The rising edge of the pulse usually evolves from far to near gauss distribution. The phenomenon is called as the field evolution of the pulse risin g edge.