Abstract: In order to take full use of waste resources，the waste Pleurotus ostreatus compost was selected to extract and process high-purity cellulase by orthogonal optimization，ammonium sulfate precipitation，dialysis and aqueous two-phase extraction method. Results showed that the specific activity，purification fold and recovery rate of the resultant enzyme was 19 705.60 U/mg，5.34 and 60.9%，respectively，after using 0.2 mol/L acetic acid-sodium acetate as buffer solution（pH 5.5），ratio of material to liquid at 1∶4，immersing for 1-2 h at 15℃ and extraction by aqueous twophase system composed of PEG6000 and ammonium sulfate with mass fraction of 20%.