The invention discloses a preparation method of tenofovir, which comprises the following steps: 1)(R)-9-(2-hydroxypropyl)adenine shown in a formula (III) is subjected to an acylation reaction through an acyl chloride/carboxylic acid system to synthesize (R)-9-[2-(alkanoyloxy)propyl]adenine shown in a formula (IV); wherein, R is methyl or ethyl; 2)in an organic solvent, (R)-9-[2-(alkanoyloxy)propyl]adenine is exchanged with magnesium methoxide to magnesium salt shown in a formula (X), diethyl (tosyloxy)methylphosphonate (short for DESMP) shown in a formula (VIa) is added for condensation to generate tenofovir diethyl ester shown in a formula (Va); and 3) tenofovir diethyl ester is passed through trimethyl bromo silicane to remove ethyl to obtain the tenofovir shown in a formula (I). The preparation method of tenofovir has the advantages of high yield, low cost of raw material and convenient operation, and is suitable for industrial production.