Abstract: Adefovir dipivoxil contains two crystal forms of A and E by analysis of Fourier transform infrared spectroscopy(FTIR)and X-ray diffractometer(XRD). It is certified that the Quantitative Analysis of Crystal forms of Adefovir dipivoxil can be used by the method of Differential Scanning Calorimetry(DSC).The method is based on the principle that different crystal forms show the different melting point and molten enthalpy. The molten enthalpy is corresponding to the amount of the crystal form. It is a useful and rapid method of guiding the production technology and the control of product quality.