In order to solve the problem about the serious waste of water resources for irrigation in litchi orchard, a fuzzy expert system was designed based on wireless sensor network according to the existing equipment conditions, and the fuzzy controller was optimized in order to improve the performance of this system. In this system, the environment information of litchi orchard was collected from sensor nodes through gateway nodes in real time. The error and changing rate of measured water content of soil and optimum moisture content of soil were selected as the decision factors and the results of forecasting irrigation values were obtained. The effectiveness of the system was analyzed by Matlab simulation and field test. Simulation results showed that this intelligent irrigation system based on the basic fuzzy controller can be combined with the timely and proper irrigation and it realized the economic irrigation effectively. And the optimized fuzzy irrigation system had better transient performance, control precision and anti-jamming, and the system response time was faster. Test results showed that the intelligent irrigation system based on the basic fuzzy controller can control the irrigation in litchi orchard effectively. It kept the soil moisture content at 17.8% in litchi orchard, which was good for the growth of litchi. The intelligent irrigation system based on the optimized fuzzy controller was able to control the average soil moisture content in litchi orchard at 17.6%, which was closer to the optimal soil moisture content of litchi orchard in the system. And it had a higher control accuracy, as well as stronger anti-interference and practicality.