The invention belongs to the technical field of wet metallurgy and resource recycling, and provides a method for detoxifying chromium slag and recycling a compound by hydrothermal reduction through abandoned biomass. The method comprises the following steps: displacing a hexavalent chromium solution by using a displacement solution with the similar ion radius under the alkaline condition at first;detoxifying hexavalent chromium in a reduction manner by using biomass such as cotton stalk as a polysaccharide carrier and a carbon source to replace the traditional methanol, starch and the like; and collecting a recyclable chromium compound while assisting in a hydrothermal process to accelerate reduction reaction. By the method, alkaline leached over-low chromium slag is fixed by hydrothermalreduction through biomass residues, the problem of chromium slag pollution is solved fundamentally, moreover, the problem of acid corrosion is solved, meanwhile, the biomass replaces a traditional reducing agent, chromium is recycled, and chromium resources are recycled while the detoxifying cost is reduced.