NOVELTY - Preparing modified biomass activated coke adsorbent for removing mercury, comprises: (1) mixing the biomass and phosphoric acid; (2) filtering the obtained biomass liquid-solid mixture, drying to obtain biomass particles; (3) impregnating biomass pellet and processing; (4) taking out the obtained activated material; (5) mixing hydrogen halide ammonium salt and biomass activated coke; (6) filtering the solution, and drying the obtained biomass activated coke, to obtain the modified biomass activated coke for removing mercury adsorbent.    USE - The method is useful for preparing modified biomass activated coke adsorbent for removing mercury (claimed).    ADVANTAGE - The method is convenient and simple, has little pollution and convenient for industrial popularization.    DETAILED DESCRIPTION - Preparing modified biomass activated coke adsorbent for removing mercury, comprises: (1) mixing the biomass and phosphoric acid according to the mass ratio of 1:3, biomass particles of about 100 meshes with granularity of 20% are immersed in phosphoric acid solution, and using a magnetic stirrer to continuously stir for 12-24 hours, obtaining biomass liquid-solid mixture; (2) filtering the obtained biomass liquid-solid mixture in step (1), drying at a temperature of 45-50 degrees C to obtain biomass particles; (3) under nitrogen (N2) atmosphere, impregnating biomass pellet and processing at 400-600 degrees C and pyrolyzing for 30-90 minutes to obtain the activated material; (4) taking out the obtained activated material, and using de-ionized water until the pH value of the washing liquid is 6-7, drying at 45 degrees C to obtain the activated biomass; (5) mixing hydrogen halide ammonium salt and biomass activated coke at a ratio of 100:1, providing ammonium halide salt solution, and using a magnetic stirrer to continuously stir for 2 hours; (6) filtering the solution obtained in step (5), processing the biomass activated coke and halogenated ammonium salt solution liquid-solid mixture, and drying the obtained biomass activated coke at 45 degrees C, to obtain the modified biomass activated coke for removing mercury adsorbent. An INDEPENDENT CLAIM is a modified biomass activated coke removing mercury sorbent.