The present invention relates to a fluidized-bed catalyst for propylene ammoxidation to produce acrylonitrile, which consists of silica support and a composite of the formulaA.sub.a B.sub.b C.sub.c Ni.sub.d Co.sub.e Na.sub.f Fe.sub.g Bi.sub.h M.sub.i Mo.sub.j O.sub.xwherein A is potassium, rubidium, cesium samarium, thallium, or mixture thereof; B is manganese, magnesium, strontium, calcium, barium, lanthanum, rare earth, or mixture thereof; C is phosphorus, arsenic, boron, antimony, chromium, or mixture thereof; M is tungsten, vanadium, or mixture thereof. The catalyst of the present invention is highly active and selective for preparing acrylonitrile, more specifically, is suitable for catalyzing the reaction between air and propylene at a rather low ratio hence to greatly enlarge the processing capacity of the reactor. By using the catalyst of the present invention, the processing capacity of the reactor increases by 10-15 percent compared with that using conventional catalysts.