The invention discloses a cadmium-arsenic absorbing material and a preparing method and application thereof. The cadmium-arsenic absorbing material includes the steps that biomass is smashed and heated to 500 DEG C quickly under the limited oxygen or oxygen-free condition, then thermal cracking is conducted till the biomass is totally carbonized, the biomass is cooled naturally to the room temperature, smashing is conducted, and an absorbing material precursor is obtained; the absorbing material precursor is mixed with a ferric salt solution, a mixture of the absorbing material precursor and the ferric salt solution is prepared, the mixture is placed at the temperature of 110 DEG C to 150 DEG C to conduct reaction for 12 hours and then is cooled to the room temperature, dissociative ferric salt remaining on the surface of the material is washed out, and the cadmium-arsenic absorbing material is obtained after being dried at 80 DEG C. The cadmium-arsenic absorbing material and the preparing method and application can be used for absorbing cadmium and/or arsenic and restoring soil or water polluted by heavy metal; secondary pollution is avoided; the soil physicochemical property is improved; meanwhile, biomass waste is converted into a soil restoration material, the cadmium-arsenic absorbing material is low in cost and wide in source, and the soil restoration cost is lowered.