The invention provides an immobilized heteropoly acid ionic liquid catalyst for liquid phase Beckmann rearrangement reaction and a preparation method thereof. A carrier is graphene oxide (GO) powder prepared by a modified Hummers chemical method. The method comprises the following steps: firstly performing condensation reaction between GO and a silane coupling agent, then performing alkylation reaction with imidazole, successively sulfonating with alkyl sultone and finally performing disproportionated reaction through Keggin structure heteropolyacid. The immobilized heteropoly acid ionic liquid catalyst provided by the invention firstly utilizes GO as the carrier, and heteropoly acid ionic liquid with a sulfonic acid group is immobilized on the surface of the catalyst through a chemical grafting method. The preparation method provided by the invention has the benefits that raw materials are easy to obtain, the catalyst is simple to prepare, a solvent can be recycled after the catalyst is used, and almost no pollution is caused to the environment. The synthesized catalyst is applied to the liquid phase Beckmann rearrangement reaction; the catalyst is convenient for separation and recovery operation, and long in service life, so that the use cost is greatly reduced; therefore, the catalyst becomes a green chemical novel catalytic material with an application prospect.