Abstract: Malvern Laser Particle Size Analyzer is a commonly used instrument to measure the particle size distribution of Arizona test dust. The sample size distribution was characterized by both dry and wet methods using Malvern Mastersizer (MS2000). The results show that for different particle sizes, the dry method results have good repeatability, but the sample was used in a large amount. Although the wet test uses a small amount of sample, when there are large particle sizes in the sample, the large particle sizes tend to settle in the solution and are not easily mixed, making it difficult to be absorbed into the detector, resulting in poor repeatability of the measurement results, and the particle size (D₅₀) corresponding to the cumulative percent size distribution up to 50% of the test obtained was significantly different from that of the dry method. By grinding A2 dust to reduce the particle size distribution from 1～100 μm to 1～50 μm, the repeatability of the wet test was greatly improved and was comparable to that of the dry method, which is close to that of the dry method, including the D₅₀.