The degree of substitution of hydroxypropyl beta cyclodextrin is the relative content of hydroxypropyl in hydroxypropyl beta cyclodextrin, and there are three positions that can be replaced per glucose residue, which means that the maximum molecular substitution degree of total substitution is 21, and the minimum is 1. In the preparation of hydroxypropyl beta cylodextrin, it is often difficult to control a fixed degree of substitution. Therefore, the average degree of molecular substitution of hydroxypropyl beta cylodextrin from different sources is different. Due to different degrees of substitution of hydroxypropyl beta cylodextrin, various performance parameters are also slightly different. For example, hemolytic, hygroscopic and solubilizing capacity decrease with increasing degree of substitution.