The invention discloses a preparing method of a magnetic hydrogel microsphere, and belongs to the field of sewage treatment. The method includes firstly preparing graphene oxide (GO@Fe<3>O4) loaded with Fe<3>O4 magnetic nanometer particles through a coprecipitation process, mixing the GO@Fe<3>O4 with a water soluble polymer (such as sodium carboxymethylcellulose (CMC)), and preparing the magnetic composite hydrogel microsphere (such as CMC/GO@ Fe<3>O4) through a spray drying process. The prepared composite hydrogel microsphere has good swelling properties and a large specific surface area. The adsorption efficiency for pollutants is increased, and pollutant adsorption varieties and adsorption amounts of hydrogel are increased. The composite hydrogel microsphere is easy to separate, and can be adopted as adsorbents for organic dye and heavy metal ions in industrial waste water.