The invention discloses a preparation method of a magnesium-hydroxyapatite adsorbent, characterized in that calcium nitrate, magnesium nitrate and ammonium phosphate are used as raw materials and distilled water as a solvent to prepare a precursor solution, the precursor solution is evenly mixed into white precipitate by chemical precipitation, and the white precipitate is centrifugally washed many times, dried at 80 DEG C and thermally treated at 600-800 DEG C to obtain the magnesium-hydroxyapatite adsorbent. The magnesium-hydroxyapatite adsorbent for adsorbing wastewater heavy metal ions is prepared by using the low-price calcium nitrate, magnesium nitrate and ammonium phosphate as a precursor via chemical precipitation process easy to perform; compared with other preparation methods, the preparation method is simple and is low in cost.