Abstract: Phosphogypsum contains soluble phosphorus, which limits the application of phosphogypsum in building materials. Using quicklime as a modifier, the content of soluble phosphorus in phosphogypsum under different mass ratio of quicklime/phosphogypsum and different calcination temperatures were studied. X-ray diffraction, field emission scanning electron microscopy, acidity-basicity analyzer and laser particle size analyzer were used to analyze and compare the phase composition, micro-morphology, acidity-basicity and particle size distribution of phosphogypsum before and after calcination. The results showed that all gypsum in phosphogypsum was converted to bassanite when the calcination temperature was between 100℃ and 200℃. The surface of the phosphogypsum crystal was damaged, which caused the soluble phosphorus content to increase gradually with the calcination temperature. Since quicklime can promote the conversion of soluble phosphorus into insoluble substance, the soluble phosphorus in phosphogypsum can be reduced effectively after adding the modifier of quicklime. The content of soluble phosphorus decreased with quicklime dosage. Phosphogypsum with a slight content of soluble phosphorus can be obtained by modifying and calcining. This will provide new guidance for the resource utilization of phosphogypsum.