The invention provides a phase transfer catalyst, a preparation method thereof and a method for preparing glutaric acid by use of cyclopentene and relates to the field of preparation of chemical catalysts. The preparation method of the phase transfer catalyst comprises the following steps: mixing tungstic acid with 30-40% of hydrogen peroxide; heating the mixture to 40-90 DEG C for dissolution; cooling the solution; mixing the solution with phosphoric acid to obtain a phosphotungstic acid solution; performing a mixing reaction on the phosphotungstic acid solution and a water solution of quaternary ammonium salt hexadecylpyridinium chloride for 50-70 min to obtain a sediment; and performing drying after filtering. As lots of toxic organic solvents are not used, the method is environmentallyfriendly; and the prepared phase transfer catalyst is good in uniformity and stable in structure. The method for preparing glutaric acid by use of cyclopentene comprises the following steps: mixing the phase transfer catalyst with hydrogen peroxide; dripping cyclopentene while stirring; and performing a reaction for 12-20 h, wherein the reaction has the advantages of high reaction efficiency, high product yield and high catalyst yield.