Abstract: Calcium sulfate whisker (CSW) with different length-diameter ratios was prepared under different reaction conditions and then it was dry-modified with silane coupling agent KH550(2% of CSW quality) at 110 ℃ for 1 h. Then PP/CSW composites were prepared for testing. The mechanical properties and the differential scanning calorimetry(DSC) analysis results show that the CSW with different length-diameter ratios have improved mechanical and crystallization properties of PP; the tensile strength and the flexural modulus of the composite with 20%(mass fraction) modified CSW with the length-diameter ratios of 29 were 11% and 104% respectively; the crystallization temperature is 12 ℃ higher than that of pure PP; the several types of CSW have all improved thermal stability and heat resistance of the composite, and with the increase of content of the whisker, the thermal stability and heat resistance of the composites improved more significantly.