A vanadium-based catalyst comprises an active phase carried on a carrier. The active phase comprises vanadium oxide, potassium sulfate, sodium sulfate, and assistants. The carrier comprises ultra-large-pore silicon dioxide and diatomite, the average pore size of the ultra-large-pore silicon dioxide ranges from 100 nm to 500 nm, and the diatomite is a refined diatomite having a silicon dioxide content of higher than 85% after refinement. The preparation method for the vanadium-based catalyst comprises: 1) mixing potassium vanadium and potassium hydroxide, and allowing a prepared mixed solution and sulfuric acid to carry out a neutralization reaction; and 2) mixing a neutralization reaction product in step 1) with the carrier and sodium sulfate, and carrying out rolling, band extrusion, drying and roasting to prepare the vanadium-based catalyst, assistant compounds being added in step 1) and/or step 2).