The invention discloses benzoic acid modified polyvinyl butyral and a preparation method and application thereof. The benzoic acid modified polyvinyl butyral is prepared by uniformly mixing 12 to 20 mass percent of benzoic acid, 1 mass percent of catalyst, 0.05 to 0.5 mass percent of antioxidant, 2 to 5 mass percent of maleic anhydride graft and the balance of polyvinyl butyral, and putting the mixture into an extruder for reaction and extrusion, wherein in the extruder, the temperature of a feeding area is 140 DEG C, the temperature of a plasticizing area is 155 DEG C and the temperature of a discharge hole is 140 DEG C. The preparation method is simple; and the prepared modified polyvinyl butyral has better elasticity, can replace a thermoplastic elastomer in practical application and overcomes the defect that the conventional polyvinyl butyral (PVB) has insufficient elasticity.