Phosphogypsum (PG) is a solid waste (by-product of the "wet process" phosphoric acid production) in phosphate fertilizer industry which is environmentally harmful. This paper studies purification of calcium oxide in the PG decomposition residue. The phase and the spectral signature of the purified sample were characterized and analyzed by XRD, SEM, and EDS. The experimental results indicate that impurities in the residue are effectively removed by sucrose solution. The reactions between calcium oxide and sucrose solution are well explained. In the purification process, soluble calcium sucrose is produced and almost all the impurities which are insoluble in sucrose solution are removed by filtration. Then the calcium carbonate synthesized by calcium sucrose and CO2 is calcined at 1173.15 K for 2 hours and the optimum mass ratio of the decomposition residue and sucrose solution is 5:100. It was concluded that the content of calcium oxide in the calcined products increased to 98.15% and it also had a compact structure, well-proportioned surface, and higher whiteness.