The invention relates to the field of chemistry, and particularly relates to a preparation method of valine acyclovir. The preparation method comprises the following steps: A, adding acyclovir and CBZ-L-valine to an N,N-dimethyl formamide solution, controlling the temperature between 20 DEG C and 30 DEG C, adding a reaction additive, and reacting for the time of 10-15 hours to obtain X2 and X3 reaction liquid; B, adding carbon powder to the reaction liquid, reducing the temperature to 0+/-2 DEG C, filtering to remove an X3 substance, and concentrating, crystallizing and purifying filter liquor which contains X2 to obtain the X2; C, drying the X2 obtained from the step B, then dissolving the X2 into an organic solvent, adding a palladium carbon catalyst, introducing hydrogen, reacting at 20-25 DEG C for 5-10 hours, filtering after the reaction is finished, concentrating the filter liquor, and then crystallizing and purifying to obtain an X1 target product. The preparation method disclosed by the invention has the advantages of easiness for operation, cleanliness, environmental friendliness, high yield and small equipment investment.