This invention introduces a method of preparing a carbon-based sulfur-loading iron-containing adsorbent for mercury removal, which can solve the problems in the prior art that sulfur-rich heavy organic materials have low-value utilization and the elemental mercury in atmosphere is hard to be efficiently and economically removed by the existing mercury removal agents. A carbon-based sulfur-loading iron-containing adsorbent for mercury removal is prepared in this invention. The adsorbent with a porous structure is prepared in situ by performing steps such as chemical activation of sulfur-rich heavy organic materials that are rich in iron. The adsorbent prepared herein has good mercury removal performance in simulated coal-fired flue gas. This invention not only improves the utilization value of sulfur-rich heavy organic materials, but also prevents SOX pollution caused by the combustion of sulfur-rich heavy organic materials and controls mercury pollution in the coal-fired flue gas.