The invention belongs to the technical field of synthetic rubber, and relates to an isoprene rubber grafted maleic anhydride and a preparation method thereof. The isoprene rubber grafted maleic anhydride comprises, by mass, 84.7-91% of isoprene rubber, 3.4-3.6% of an initiator and 5.4-11.9% of maleic anhydride. The preparation method comprises the following steps: fully dissolving isoprene rubber in a solvent under normal pressure, adding a maleic anhydride monomer, adding benzoyl peroxide, and continuously stirring and reacting for a period of time; precipitating the above obtained product by using acetone after the reaction ends, carrying out suction filtration, and drying the obtained product; and extracting the dried product in acetone for 3h, purifying the extracted product, and carrying out vacuum drying to obtain the isoprene rubber grafted maleic anhydride. The isoprene rubber grafted maleic anhydride polymer is successfully prepared; the isoprene rubber grafted maleic anhydride has the advantages of light peculiar smell, white color, environmental protection and safety; and the preparation method has the advantages of simple process, easily controlled conditions, low cost, low device requirements, and suitableness for industrial production.