The invention relates to a method for producing sulfuric acid and co-producing calcium carbide by phosphogypsum, and belongs to the technical field of environmental protection. According to the method, phosphogypsum is subjected to a water washing and purification pretreatment by a multi-stage cyclone; then the pretreated phosphogypsum is dried and dewatered; the dewatered phosphogypsum enters a multi-stage suspension heat exchanger to carry out preheating; the hot state gypsum enters a circulating fluidized bed decomposing furnace, then primary air and secondary air are respectively introduced to carry out decompositions; high temperature sulfur dioxide-containing flue gas discharged from the top of the circulating fluidized bed decomposing furnace enters the multi-stage suspension heat exchanger to carry out heat exchanging and cooling with the cold state gypsum; dust in the cooled hot flue gas is removed by a multi-stage dust removing device; the dust-removed flue gas enters an acid washing and purification system to further remove the dust and the gaseous impurities in the flue gas; the purified and cleaned flue gas is conveyed into an acid preparation system to produce the sulfuric acid product; the hot state calcium oxide discharged from the bottom of the circulating fluidized bed decomposing furnace is cooled, and conveyed into a sealed calcium carbide furnace to carry out an electrical arc reaction with a carbon material to generate the calcium carbide product; the high temperature furnace gas discharged from the top of the sealed calcium carbide furnace is directly conveyed into the decomposing furnace, wherein the high temperature furnace gas is adopted as a fuel and a reducing agent. The method of the present invention has good environmental protection benefits and strong economic advantages.