Abstract: With the development of modern agriculture toward precision pesticide application, green plant protection, and pesticide reduction with improved efficiency, spray application has been widely used in agricultural plant protection, and its operational performance and environmental safety have attracted increasing attention. Droplet size and velocity distributions generated by spraying are key parameters for characterizing spray performance, and their spatial distributions directly affect pesticide deposition efficiency, spray coverage uniformity, and spray drift risk. Therefore, measuring and analyzing droplet size and velocity characteristics is of great significance for agricultural nozzle development and adjuvant screening. In this study, a six-element grid method for measuring droplet size and velocity distributions in the atomization space was established based on phase Doppler interferometry (PDI). Water, 0.075 wt% polyethylene oxide (PEO), 0.5 CMC PEO/sodium dodecyl sulfate (SDS), 1 CMC PEO/SDS, 2 CMC PEO/SDS, and 4 CMC PEO/SDS were selected as spray solutions. The surface tension and viscosity of the six spray solutions were measured. The spatial distribution patterns of droplet size and droplet velocity produced by a flat-fan pressure nozzle under different spray pressures were measured and analyzed, with the aim of providing theoretical support for agricultural nozzle development and adjuvant screening. The results showed that the addition of PEO and SDS significantly increased solution viscosity and decreased surface tension. In the PEO/SDS system, the surface tension of the four solutions tended to stabilize, whereas viscosity continued to increase with increasing SDS concentration. Compared with water, the surface tension of the 4 CMC PEO/SDS solution decreased by 64.3%, while its viscosity increased by 408.99%. Increasing spray pressure reduced droplet size, whereas increasing solution viscosity increased droplet size and decreased the cumulative volume fraction of small droplets. Fractal dimension (FD) analysis further revealed the effects of solution properties and spray parameters on droplet size distribution. FD increased with increasing spray pressure and solution viscosity. At a spray pressure of 200 kPa, when solution viscosity increased from 0.89 mPa·s to 4.53 mPa·s, the FD value increased from 1.67 to 2.10, representing an increase of 25.7%. At a spray pressure of 250 kPa and the measurement point of X = 0 and Z = 272 mm, the cumulative volume fraction of drift-prone droplets (<100 μm) for 4 CMC PEO/SDS was 70.6% lower than that of water. A comprehensive comparison of the six solutions showed that 4 CMC PEO/SDS had the most pronounced effect in reducing the proportion of drift-prone droplets and exhibited a relatively high FD value. Analysis of droplet velocity characteristics showed that droplet horizontal velocity generally increased with increasing horizontal distance from the nozzle. A strong correlation was observed between radial horizontal velocity and horizontal distance, with the coefficients of determination (R²) of the fitted curves exceeding 0.8 under all solution conditions, indicating that the spatial variation patterns of droplet velocity were relatively stable and consistent. Spatial distribution analysis further showed that droplet velocity and kinetic energy were higher in regions close to the nozzle than in regions farther from the nozzle. In addition, droplets near the edges of the spray plane generally exhibited higher velocity and kinetic energy than those near the spray axis. Under different solution conditions, droplet velocity and kinetic energy showed consistent distribution patterns across the spray plane, and both increased with increasing solution viscosity. In summary, the six-element grid method for measuring droplet size and velocity distributions in the atomization space established in this study based on PDI can provide fine-scale characterization of the spatial distribution patterns of droplet size and velocity generated by pressure nozzle atomization, enabling synchronous measurement and analysis of droplet size and velocity. This method helps reveal the spatial non-uniformity and variation trends of droplet distributions across the spray plane, and provides methodological and data support for agricultural nozzle development, spray atomization characterization, and adjuvant screening and optimization.