With SiO₂ as the carrier and decanoic acid-palmitic acid as a phase change material, nano decanoic acid-palmitic acid/SiO₂ phase change and humidity storage composite materials were prepared by the sol-gel process. The effects of solute concentration, ultrasonic dispersing power, ultrasonic dispersing time and dispersant concentration on the particle size distribution of composite materials were investigated using the particle size d₅₀, d₉₀, d₁₀ and d₉₀-d₁₀ as evaluation indicator. The results indicated that the laser particle size analyzer (test range 1~10000 nm) is applicable to the particle size measurement of nano decanoic acid-palmitic acid/SiO₂ phase change and humidity storage composite materials showing high reproducibility. Optimum dispersion conditions are solute (composite material) concentration 4 g/L, ultrasonic dispersing power 300 W, ultrasonic dispersing time 30 min, dispersant sodium hexametaphosphate concentration 3 g/L.