The invention discloses a catalyst and a preparation method thereof. The method comprises: (i) providing a catalyst precursor having the following general formula, wherein A is at least one element selected from potassium, sodium, rubidium and cesium, X is at least one element selected from nickel, magnesium, zinc, chromium, manganese, tin and lead, Y is at least one element selected from germanium, cerium, niobium, tungsten and antimony, Z is at least one element selected from silicon, titanium, aluminum and zirconium, a is more than or equal to 0.5 and is less than or equal to 8, b is more than or equal to 0.1 and is less than or equal to 8, c is more than or equal to 0.1 and is less than or equal to 5, d is more than or equal to 0.01 and is less than or equal to 2, e is more than or equal to 0.01 and is less than or equal to 4, f is more than or equal to 0 and is less than or equal to 1, g is more than or equal to 0 and is less than or equal to 2, and h is the required oxygen atom ratio satisfying the atom valence of various elements; and (ii) uniformly mixing the catalyst precursor and a sulfur-containing compound, molding, and carrying out calcining activation for 1-10 h at a temperature of 300-600 DEG C to obtain the catalyst, wherein the amounts of the catalyst precursor and the sulfur-containing compound make the ratio Z (y/x) of the amount x of the composite oxide derived from the catalyst precursor to the amount y of the sulfur element derived from the sulfur-containing compound be more than or equal to 0.01 and less than or equal to 2. Mo10CoaFebBicAdXeYfZgOh.