Abstract: Modified the mixing fly ash and pyrite cinder by hydrochloric acid，and the compound modified product was applied to adsorb the hexavalent chromium in waste water． The preparation conditions of the composite modified product were: Ash ratio is 10∶ 1，the concentration of hydrochloric acid was 30%，modified time was 1 h in the boiling state． When the hexavalent chromium concentration was 5 mg /L，pH was 6，and the adsorbent dosage was 40 g /L，the adsorption reaction temperature was 10 ℃， the adsorption reaction reached balance after 1 h with the adsorption efficiency of more than 97%． This adsorption reaction conformed to Langmuir isothermal equation and Freundlich isothermal equation，which was synergistic reaction of physical adsorption and chemical adsorption． Research showed that the compound modification method was low-cost and easilyoperated and was suitable to dispose chromium-containing wastewater at a low concentration，contributing to the resource utilization of solid waste．