The invention discloses a catalyst for preparing maleic anhydride by n-butane oxidation and a preparation method and application thereof. According to the invention, diatomite is used as a carrier; ageneral formula of active components is that: V1.0PaMobOm, wherein a is within a range of 0.8 to 1.6, b is within a range of 0.05 to 0.5, m represents the number of oxygen atoms required for meeting the valence of each element. The catalyst is prepared by adopting a deposition-precipitation method, and the main application and advantage of the prepared catalyst are that under the low-pressure condition, an oxidizing reaction of preparing the maleic anhydride by the n-butane has higher activity.