The invention discloses a vanadium-phosphorus-oxide catalyst and a preparation method thereof. In the vanadium-phosphorus-oxide catalyst, (VO)2P2O7 content is 80-95% by metering with volume, the vanadium-phosphorus-oxide catalyst has dual tunnels distribution with the apertures of 10-20 nm and 20-35 nm, wherein the tunnel with 10-20 nm accounts for 29-36% of total tunnel volume, and the tunnel with 20-35 nm accounts for 34-45% of total tunnel volume. The preparation method comprises the following steps: an ionic liquid I and an ionic liquid II are added in a synthesis process, after the reaction is completed, a generated precipitate is subjected to filtering, drying and roasting to obtain a vanadium-phosphorus-oxide catalyst precursor, and the vanadium-phosphorus-oxide catalyst precursor is subjected to activation moulding to obtain the catalyst. The vanadium-phosphorus-oxide catalyst has dual tunnels distribution, and can be taken as n-butane for preparing maleic anhydride through oxidation, n-butane conversion rate is high, and maleic anhydride selectivity is good.