To overcome the poor hydraulic performance problem of impact sprinkler when operating at low pressure, a program of modifying the shape of outlet nozzle was put forward. It was used to reduce the droplet impact strength and improve the uniformity coefficient. Impact sprinkler typed PY115 was chosen and three improved nozzles were designed. One, two or three notches were to be added in the outlet nozzle, respectively. All the notches were 0.5 mm in width and 0.3 mm in height and they were set at bottom, left or right side of the outlet nozzle. Experiments were carried out under the low operating pressure of 200kPa. When the rectangular spaces were 13m to 18m, Matlab was used to establish a program to simulate the hydraulic performances. The results showed that with the increase in the number of notches, the flow-rate increased, the wetted radius were shortened by 8.1% to 9.4%, the reduced coefficient of droplet diameter was 2.9% to 6.8%, the average irrigated intensity increased and complied with national requirement. The combined uniformity coefficient was improved for all the improved nozzles. The effect was more obvious when three notches were added in the outlet nozzle and the maximal uniformity coefficient can be more than 90％. Modifying nozzle shape was proved to be an available program as a result.