The invention discloses an arsenic resistant catalyst for preparing sulfuric acid by oxidizing sulfur dioxide and a preparation method thereof. The arsenic resistant catalyst is used for preparing acid from nonferrous metal refining smoke and pyrite with high arsenic and fluorine content. A vanadium catalyst is added with calcium salt, tin salt and aluminum salt, and diatomite is subjected to water separation, acid treating, filter pressing and drying to prepare a carrier; potassium hydroxide and vanadium pentoxide are dissolved and purified in proportion to prepare mixed solution; the mixed solution is neutralized by sulfuric acid to prepare a V2O5 and K2SO4 colloid mixture, and colloid precipitate is subjected to standing and osmosis; and the colloid precipitate, the calcium salt, the tin salt, the aluminum salt and the diatomite are added into a roller, mixed evenly, and ground into a plastic material, and the plastic material is formed, dried, baked, sieved and packaged into the vanadium catalyst. Through formula adjustment and the increase of a standing and osmosis process, the materials are more evenly mixed, the strength, arsenic resistant antitoxic performance, service life and stability of the catalyst are improved, the arsenic resistant antitoxic capacity of the catalyst is 3 to 4 times higher than that of the conventional catalysts, and the SO2 conversion rate is stably kept above 99.6 percent.