Spraying is the most widely used means of pesticide application for pest control in agriculture and forestry. The atomization characteristics of the nozzles are directly related to the spray drift, rebound, and deposition. Previous research studies have mainly focused on the change pattern of atomization characteristics. Mathematical descriptions of the atomization characteristics of flat fan nozzles are rare, and pesticide application theories are also insufficient. Atomization characteristics mainly include droplet size and velocity. This study analyzes the influence of the spray parameters (spray angle, pressure, and equivalent orifice diameter of nozzles) and the spatial position in the flow field. To obtain the atomization characteristics of flat fan nozzles, the phase Doppler particle analyzer (PDPA) was selected for the accurate measurement of the droplet sizes and velocities at distances 0.30–0.60 m, using low spray pressures (0.15–0.35 MPa). The droplet size and velocity models were then established and validated. The results revealed that the average absolute error of the droplet size model was 23.74 µm and the average relative error was 8.23%. The average absolute and relative errors of the droplet velocity model were 0.37 m/s and 7.86%, respectively. At a constant spray pressure and angle, there was a positive correlation between the droplet size and the equivalent orifice diameter of the nozzles. The test also verified that the spray angle and distance had a negative correlation with the droplet velocity at a given pressure. The spray distance had no effect on the spray axial droplet size at constant spray pressure. In addition, the spray angle greatly affected the droplet velocity along the X-axis; similarly, the spray parameters, especially spray angle, greatly affected the droplet size.