The invention relates to a preparation method of an SBA-15-based silver-loaded adsorbent for flue gas demercuration of coal-fired power plants, belonging to the technical field of environmental protection and atmosphere pollution control. The preparation method mainly comprises the steps of adding mesoporous silica SBA-15 into a silver-ammonia solution, and dipping to obtain a precursor; then, carrying out thermal reduction on the precursor in an inert atmosphere to obtain the SBA-15-based demercuration adsorbent loaded with nano-silver particles. The preparation method is simple and reliable, free from silver loss, does not use a reducing agent, and is low-cost and easy for industrial application. The adsorbent prepared by method is relatively large in specific surface area, and contains the silver particles which are maintained in a nanoscale, and high demercuration efficiency, large demercuration capacity and simple regeneration are achieved; the demercuration efficiency and capacity of a regenerated adsorbent basically are not obviously decreased, so that the adsorbent can be recycled, and the application cost is lower. Therefore, the SBA-15-based silver-loaded adsorbent is a demercuration material having industrial application prospect.