Lithium chloride was used to induce protoplasts of Aspergillus niger.Mutation strain with higher phytase content was screened in this paper.The optimized isolation method for protoplasts from Aspergillus niger was obtained.The results showed that the suitable conditions were cellulose 1%,snailase 0.5%,mycelium age 24h,enzymatic hydrolysis temperature 30℃,time 2h and osmotic pressure stabilizer 0.7 mol/L sodium chloride.Lithium chloride was used to induce the protoplasts.The results showed that the survival rate of strains was 23.3% induced with 0.15% Lithium chloride.And one strain with the highest enzyme activity of 19.24 U/mL was obtained,and the enzyme activity has a 54.41% increase compared with the original strain.Heredity of induced strains was stable.