The invention discloses a method for preparing corrosion-resistant biological magnesium alloy. The method comprises the following steps: (1) putting calcium oxide powder and biological magnesium alloypowder in a specific ratio into a ball mill, and performing ball milling under protective atmosphere so as to obtain mixed powder; and (2) performing selective laser melting under protective atmosphere by taking the mixed powder as a raw material so as to prepare the corrosion-resistant biological magnesium alloy. In the preparation process, the laser power is controlled to be 60-90W, the scanning speed is controlled to be 100-500mm/min, and the spot diameter is controlled to be 40-100mu m. According to the method disclosed by the invention, calcium oxide is added to the biological magnesiumalloy through selective laser melting so as to generate an Mg/Al-Ca phase with a smaller volume; and by utilizing the characteristic of high setting rate of selective laser melting, the volume of thesecond phase of Mg/Al-Ca is refined, and simultaneously, the continuity of Mg/Al-Ca is improved, thereby coating magnesium alloy grains to form continuous second phase protection layers to prevent thecorrosion of body fluid.