In order to explore the atomization characteristics of the LICHENG series nozzle for manned agricultural helicopter under medium and low airflow velocity conditions, droplet size tests on five sizes of nozzles—11,002, 11,003, 11,004, 11,006, and 11,010—were carried out by laser diffraction device (LDD), based on the high–low speed composite wind tunnel for agricultural aviation designed by the National Center for International Collaboration Research on Precision Agricultural Aviation Pesticides Spraying Technology (NPAAC) of South China Agricultural University (SCAU). The result showed that under the three spray pressures of 30, 40, and 50 psi, the droplet sizes of the five types of nozzles expressed similar trends with the increase of airflow velocity. Among them, the droplet size variation of nozzles 11,006 and 11,010 with larger orifice size was the most significant, the largest range of DV0.1 was of nozzle 11,010, and the largest range of DV0.5 and DV0.9 was of nozzle 11,006. In addition, the change of spray pressure would directly affect the quality of spray; especially, the nozzles 11,002, 11,003, and 11,004 with small orifice sizes were significantly affected. Under the condition of medium and low airflow velocity of 0–27.8 m/s, 89% of spread value (SV) by the five nozzles were in the range of less than 15%, but there were some test nozzles with poor spray stability during the test, which made the measurements of droplet size value larger, resulting in a maximum test deviation of up to 210.9 μm. The result also exposed that limitations exist in wind tunnel droplet size testing by using LDD, and an increase in airflow velocity resulted in a larger measurement droplet size. This phenomenon was particularly significant in the DV0.5 test results of various types of nozzles. This study can provide experimental data guidance for the optimization design and parameter selection of aerial nozzle for manned agricultural helicopter.