Magnetic porous organic polymers (MOPs) with abundant thiol groups were synthesized successfully in high yield through a template-free and catalyst-free wdiaZo-coupling reaction. The reaction was conducted under mild conditions in aqueous solution, in which the introduction of magnetism and thiol-functionalization was realized simultaneously, avoiding the use of environment-unfriendly organic solvents. The magnetic nanoparticles (MNPs) were embedded into hierarchical porous network structures of porous organic polymers (POPs) physically and the magnetism of thiol-functionalized MOPs (MOP-SH) was easily controlled by varying the amount of spiked MNPs. The obtained MOP-SH exhibited high thermal stability and chemical stability within a wide pH range (2-13), and good adsorption performance for Hg(II) over a wide pH range due to the abundant thiols in its hierarchical structure. After the adsorption process by using MOP-SH, the concentration of Hg in the spiked domestic sewage reached 1.1 mu g L-1, which is even lower than the acceptable limit of national standard for drinking water (2 mu g L-1). Besides, the prepared MOP-SH exhibited high adsorption capacity, fast adsorption kinetics, and easy-recycling behavior, providing a new avenue for the preparation of green functionalized adsorbents with good performance for water decontamination.