A method for co-producing sulphoaluminate cement and sulfur by using desulfurized gypsum and aluminum ash, comprising: (1) drying aluminum ash, and heating desulfurized gypsum for dehydration to obtain semi-hydrated gypsum; (2) mixing the aluminum ash with the semi-hydrated gypsum according to a preset ratio, pulverizing, and homogenizing; (3) calcining the pulverized and homogenized mixture of the aluminum ash and the semi-hydrated gypsum while adding coal dust to the mixture, and performing oxygen-enriched combustion to obtain a sulphoaluminate cement clinker and sulfur dioxide-containing flue gas; (4) mixing the sulphoaluminate cement clinker and the desulfurized gypsum according to a ratio, and pulverizing to obtain sulphoaluminate cement; and (5) dedusting the sulfur dioxide-containing flue gas, and performing catalytic reduction to obtain a sulfur product, wherein the mass ratio of the aluminum ash to the desulfurized gypsum to carbon powder is (33-39):(61-66):1.