The invention discloses a preparation method of a VP/alpha-olefin copolymer. The method comprises the following steps: (1), pre-activating a part of alpha-olefin to obtain a mixture A; (2), pre-copolymerization reaction: carrying out pre-copolymerization reaction on PVP (polyvinylpyrrolidone), the remaining alpha-olefin in the step (1), a compound initiating agent, an activating agent and an organic solvent at a controlled temperature of 40 to 90 DEG C to obtain a pre-copolymerized mixture B; (3), copolymerization reaction: adding the mixture A into the pre-copolymerized mixture B and controlling total reaction time of the step (2) and the step (3) to be 4 to 10 hours to obtain a copolymerized mixture C; (4), carrying out product separation on the copolymerized mixture C to obtain the VP/alpha-olefin copolymer. According to the preparation method of the VP/alpha-olefin copolymer, the temperature and the reaction time required by the copolymerization reaction can be effectively reduced, a reaction condition is mild, the reaction is easily controlled, the purity of the product is high, and complicated purification treatment on the product is not needed, so that the production efficiency is effectively improved, the production cost is reduced, and extended application of the VP/alpha-olefin copolymer is facilitated.