High power excimer laser system has its outstanding features such as short wavelength, broad bandwidth, et al. On the basis of adequate study of numbers of beam smoothing techniques in large scale laser facilities, the echelon free induced spatial incoherence (EFISI) technique is selected to accomplish the beam uniform irradiation in the angular multiplexed high power excimer laser system. In this way, measurements on dynamic uniformity of the seed beam after three paths amplification of pre-amplifier1 and double paths amplification of pre-amplifier2 with the use of partial coherence scattering seed and strict optical image relaying. Experimental results indicate that the uniformity of scattering seed is relatively kept owing to beam smoothing by EFISI technique. Typically, the nonuniformity of the beam after pre-amplifier1 amplification is 2.04%, and after pre-amplifier2 amplification is 1.96%. Meanwhile, the results mentioned above show that the technique adapts to the high power XeCl excimer laser systems.