The MCTS‐g‐AT was developed as a novel magnetic adsorbent with core‐shell structure. Its unique synthesis route endows MCTS‐g‐AT with green, convenient, economical and safe characteristics, and also good selective adsorption of Hg(II). The material was characterized using an appropriate set of spectroscopic and analytical techniques (SEM, EDS, XRD, VSM, FTIR, and TGA). Its adsorption kinetics fits the pseudo‐secondary model well and adsorption isotherm fits the Langmuir equation well, suggesting the mechanism of chemisorption with monolayer adsorption. The results of the thermodynamic parameters indicate spontaneous and endothermic process. Column adsorption experiments showed that the maximum adsorption capacity of Hg(II) was 207.6 mg/g (298 K). Moreover, the Hg(II) adsorbed on composite microspheres was completely eluted by 3 mol/L HNO3 or 4 mol/L HCl. Furthermore, MCTS‐g‐AT adsorption column combined with spectrophotometer can achieve more accurate detection of Hg(II) in aquatic products.