By analyzing the phase composition,relative crystallinity,drying compressive strength and microscopic morphology of the samples after autoclaving of phosphogypsum,the effect of autoclavic temperature,holding time,liquid-solid ratio and impurities on the preparation of α hemihydrate phosphogypsum by autoclavic compaction was studied.The results showed that the drying compressive strength of the samples obtained after autoclaving of phosphogypsum was positively correlated with the relative crystallinity of α hemihydrate gypsum crystals.When the autoclaved temperature was 130 ℃,the holding time was 3~5 h,and the liquid-solid ratio was 0.25,the obtainedα-hemihydrate gypsum had high relative crystallinity,high drying com-pressive strength,complete crystal micromorphology and small aspect ratio.Impurities in phosphogypsum would affect the me-chanical strength of autoclaved samples.After the phosphogypsum was washed with water,the α hemihydrate gypsum with a 2 h flexural strength of 7.3 MPa and a drying compressive strength of 32.8 MPa could be prepared under the conditions of au-toclaved temperature of 130 ℃,holding time of 3 h and liquid-solid ratio of 0.25,which was in line with the requirement of α30 strength grade in JC/T 2038—2010“α-type high strength gypsum”.