Abstract: According to that the sub-nozzle of impact sprinkler is circle, and the middle of radial water distribution for combination is higher, a new structure of sub-nozzle was designed based on jet flow theory. A cover plate was fixed at the top of the nozzle so that the jet water was barrieried to drop near the sprinkler, with which the combination uniformity increased. The tests of water distribution of original and improved impact sprinklers were carried out for the types of 15PY, 20PY, 30PY respectively. At the same time, the combination uniformity coefficient in different distance was calculated for square arrangement mode. The results showed that the middle part of radial water distribution was decreased than before, and the shape distribution was triangle. After the improvement, the uniformity coefficient was increased, and the value of them was over 80%. The sprinkler irrigation intensity was accorded with sprinkler irrigation standard. Finally, the combination distances of the types of 15PY, 20PY, 30PY were 1.2R, 1.3R, 1.1R after improvement, and the combination uniformity coefficient values were 85.6%, 86.3%, 85.3% respectively. The new structure of sub nozzle improved the combination uniformity observably.