The invention provides a preparation method of kyprolis, which comprises the steps of carrying out a
condensation reaction among N-Boc-L-homophenylalanine shown in a formula (I), L-
leucine ester shown in a formula (III) and salt, and carrying out
deamination protection so as to obtain a compound shown in a formula (V); carrying out a
condensation reaction between the compound shown in the formula (V) and morpholin-4-yl-
acetic acid shown in a formula (VI), and carrying out
decarboxylation protection so as to obtain a compound shown in a formula (IX); carrying out a
condensation reaction between the compound shown in the formula (IX) and a compound shown in a formula (VIII), so that kyprolis is directly generated. According to the invention, a
convergent synthesis method is adopted, and condensation and deprotection among amino acids are only involved, so that the reaction steps are less,
reaction conditions are mild and controllable, and the yield of kyprolis is increased, therefore, the method is suitable for industrial production. Experimental results show that by using the method provided by the invention, the yield of kyprolis can reach 19.3-30.8%.