The invention relates to an extraction method of mangrove plant DNA, comprising the following steps: (1) taking a leaf to grind, adding preheated 2% of CTAB extract to dissolve, and then adding 2 % of PVP by volume; (2) after water bath, adding a small quantity of RNase for heat preservation, then adding chloroform-isoamylol mixed liquor, and carrying out high-speed centrifugation at normal temperature; (3) putting supernate into a centrifuge tube, adding the preheated 2% of CTAB extract, adding chloroform-isoamylol mixed liquor, and mixing and carrying out high-speed centrifugation at normal temperature; (4) taking supernate and then putting into the centrifuge tube, adding NaCl solution and cold isopropanol, mixing, and putting and precipitating DNA at low temperature; (5) carrying out high-speed centrifugation at low temperature, abandoning the supernate, recovering the precipitate, washing by ethanol, air-drying, adding TE buffer solution, and storing at low temperature. The invention can effectively remove polysaccharide and tannin produced in the DNA extraction process, and the obtained mangrove plant has high DNA content and high purity.