There are few studies on the design and optimization of liquid fertilizer sprayer, a trailed liquid fertilizer sprayer was designed, which mainly composed of tank, suction system and discharge system. The theoretical model of spraying operation was established, and the key parameters such as vacuum pump displacement, tank structure and nozzle outlet flow rate were designed and calculated. The key factors such as the shape of scattering baffle, orientation of scattering baffle, shape of nozzle and flow velocity of nozzle outlet were simulated and analyzed. The analysis showed that the ideal spraying effect can be achieved by selecting fan-shaped scattering baffle, positive angle between scattering baffle and horizontal plane, circular nozzle and outlet velocity of about 13m/s. Taking the radiation width, uniformity variation coefficient and average thickness of spraying as the spraying performance indexes, the spraying operation was optimized and simulated by orthogonal experiment. It was concluded that the significant factor affecting the spraying width was the longitudinal axis length of the scattering baffle, and the significant factor affecting the horizontal average thickness of the ground was the inclination angle of the scattering baffle, each factor had little effect on the coefficient of variation of spraying uniformity. Combined with the design goal, when the traveling speed was 5km/h, the included angle between the scattering baffle and the horizontal was 35°, the longitudinal axis length of the scattering baffle was 32cm, the outlet flow rate was 13m/s and the nozzle height was 1m. The test spraying width was 11m, the average ground thickness was 1.65mm, and the spraying uniformity variation coefficient CV was 34.86%. The simulation analysis was basically consistent with the test results, which verified the accuracy and reliability of the design. The design goal was achieved, the application requirements were met, and some data support was provided for the spraying research of liquid fertilizer.