The polymorphic i-PP，which containsa and β crystalline forms，was studied by WAXD．Asymmatrie Gause-Cauchy composite function was used to characterize the crystal and amorphous peaks．When retarded least square method was used．the results of the microcomputer multipeak resolution are rather satisfactory．When β-nucleating agent was used，the polymorphic i-PP，which contains a and β crystalline，can be pre-pared at Tc=100°-140℃．Their crystal forms，crystallinity，crystallite length and the ratio of a and β phase are dependent on Tc The results show lthat in the range of Tc，a and β phases coexisted，the reorganization of a and β crystalhtes occured，the best β-cry-sthlisation temperature is at 130℃，the change of β-content is opposite to that of the amor-phous，and the change of a-content is very small．Comcpwring the results of peak-resolu-tion with the Turner-Jones equation．an improved calculation method of ratio of a and β phases was devised．Finally．a simple calculating method of peak area in WAXD was suggested．