The invention discloses a method for preparing a selenium-rich crop cultivation medium by using domestic sludge biomass charcoal. The method is characterized by sequentially comprising the following steps: step one, preparing domestic sludge biomass charcoal; step two, preparing a selenium nutrient solution; step three, preparing selenium-rich biomass charcoal: (1) preparing selenium-rich biomass charcoal at a high temperature state; (2) preparing selenium-rich biomass charcoal at a normal temperature state; (3) mixing the selenium-rich biomass charcoal at the high temperature state with the biomass charcoal at the normal temperature state to prepare the selenium-rich biomass charcoal; step four, preparing a modified starch adhesive; step five, preparing selenium biomass charcoal particles; step six, taking and mixing the selenium-rich biomass charcoal and the selenium biomass charcoal particles, and delivering the mixture into a pelletizer for pelletizing; step seven, uniformly stirring the particles obtained in step six and crop soilless cultivation medium fillings, thus obtaining the selenium-rich crop cultivation medium. Through the selenium-rich crop cultivation medium prepared by using the method disclosed by the invention, the absorption and conversion rate of crops on the selenium element can be increased, and the selenium element can be slowly and uniformly released within a whole growth period of the crops.