The invention discloses an adefovir dipivoxil crystal form and a preparation method thereof. Cu-Ka radiation is used by the adefovir dipivoxil crystal form clear characteristic absorption peaks are generated through X-ray powder diffraction shown by 2 theta and interplanar spacing (value d), and the angle 2 theta and interplanar spacing (value d) of the absorption peaks are as follows: about 8.76(10.11), about 13.69(6.47), about 15.44(5.74), about 15.84(5.60), about 17.60(5.04), about 19.74(4.50), about 20.22(4.39), about 21.02(4.22) and about 21.73 (4.09), which is shown by angle 2 theta andinterplanar spacing (value d). The preparation process of adefovir dipivoxil of the invention is simple, the new adefovir dipivoxil crystal form with good stability is prepared; and the residual solvent in the crystal form is less than 5000ppm, thus fully conforming to the concentration limit of pharmaceutical residual solvent guidline of the International Conference on Harmonization (ICH).