In order to meet the reqirements of sprinkler irrigation uniformity and tower travelling capacity of a single-span center pivot irrigation system, the dynamics and hydraulic characteristics of the centrifugal water motor with a lower injector port were investigated. Relevant formulas were established for computing driving torque, speed and operating flow rate. The key factors affecting the driving torque and rotation speed of centrifugal water motor were analyzed. The results showed that the irrigated water depth could be adjusted more effectively by changing the working pressure of the water motor to control the rotation speed than by increasing the diameter of sprinkler nozzle to increase the work flow of water motor or by extending the length of the rotating arm. It is necessary to consider the structural and hydraulic designs of centrifugal water motor, travelling capacity and sprinkler irrigation uniformity of center pivot irrigation system simultaneously and optimize their combinations. In this way the demands of system traveling capacity and agricultural irrigation uniformity could be met at the same time.