The invention provides a method for preparing a 
mesenchymal stem cell exosome. The method comprises the steps that human 
umbilical cord tissue surface blood is cleaned to remove epidermal and vasculartissues, Wharton jelly is taken out for cleaning, then the tissues are 
cut into pieces, and 
inoculation is performed for culture; subculturing is performed; second generation of umbilical mesenchymalstem cells are inoculated and cultured; a 
cell stimulator factor for promoting 
secretion of the 
exosome is added; when the cells grow to the fusion degrees 90%, first 
cell supernate is sucked out forseparating the 
exosome; the first 
cell supernate is centrifuged to remove 
cell debris, and second cell supernate is collected; the first time of 
ultrafiltration and concentration is conducted on thesecond cell supernate, excessive 
moisture is removed, and a first concentrated solution is obtained; the first concentrated solution is subjected to the second time of 
ultrafiltration and concentration, excessive 
moisture is removed, and a second concentrated solution is obtained; the first time of ultracentrifugation is conducted on the second concentrated solution, and the supernate is taken andsubjected to the second time of ultracentrifugation, the supernate is removed, and 
precipitation is performed to obtain the exosome for 
stem cell secretion; normal 
saline is added for cleaning and 
centrifugation, the supernate is removed, and the exosome precipitate is obtained.