The invention relates to a polymerization inhibitor of a vinyl aromatic compound and its preparation method and use method. The polymerization inhibitor comprises, by mass, 5 to 30 parts of a component A, 10 to 50 parts of a component B and 100 parts of a component C. The component A is an aryl hydroxylamine compound, the component B is an acetal compound and the component C is a multi-substituted alkyl benzene compound. The polymerization inhibitor effectively prolongs the induction period of the polymerization inhibitor so as to improve the yield of the product, avoids the problems of the formation of the polymer, pipe blocking and influence on the normal operation of the production, has small toxicity and the good effect of inhibiting polymerization, removes oligomers, inhibits polymer formation, improves a distillation yield of the vinyl aromatic compound, reduces pollution and eliminates potential safety hazard.