Suspension, also known as suspended liquid preparation, refers to a heterogeneous liquid dispersion system formed by fine particles dispersed from poorly soluble solid drugs in a liquid dispersion medium. The suspension has many advantages such as accurate dosage, convenient to take, fine particle size, rapid homogenization into the human digestive tract after taking, and better effect. The way to taking medicine is more convenient, and is more suitable for infants and young children. In suspensions, drugs are dispersed into fine particles, and a deeper degree of dispersion is helpful to improving bioavailability. This is the reason why poorly soluble drugs are often made into suspensions. The principle of manufacturing of suspension is to wet the powder particles through high-pressure homogenization and homogenize them uniformly in the liquid homogenization medium, and maintain certain conditions so that they do not aggregate. The size of the particles in the suspension is not only related to the quality and stability of the suspension, but also affects the efficacy and bioavailability of the suspension. Therefore, the size and distribution of particles in the suspension are important indicators of the quality of the suspension.