The invention discloses a method for preparing a calcium carbonate raw material and SO2 by utilizing high-sulfur petroleum coke to decompose phosphogypsum, i.e., the high-sulfur petroleum coke with the carbon mass fraction higher than 80 percent and the sulfur mass fraction higher than 2 percent to 6 percent is used for reducing and decomposing the phosphogypsum to prepare burner gas with the SO2 volume percentage higher than or equal to 15 percent. The burner gas can be directly used as qualified virgin gas for the two-conversion and two-absorption acid-making technology so as to produce the solid product, CaO, with the mass fraction of higher than 50 percent, and can also be directly used as a chemical raw material, for instance, for making cement. No waste is generated in the process, the decomposition rate of the phosphogypsum is higher than or equal to 95 percent, and the desulphurization degree is higher than or equal to 90 percent. By utilizing the technology for decomposing the phosphogypsum, pretreatment is not required and the concentration of SO2 is stable in the burner gas. The content and the thermal value of carbon in the high-sulfur petroleum coke are comparatively high, and the contents of nitrogen and sulfur are higher than that of other fuels, thereby reducing reaction temperature, energy consumption and production cost, simultaneously, environment pollution is not generated and waste is changed into valuable. The utilization of components of the phosphogypsum is maximized during the technical process so as to solve the problem of realizing the harmlessness and sales of the phosphogypsum as 'dangerous waste'.