The peel of Citrus changshan-huyou, coupled with wheat bran, could be utilized by Aspergillus niger P-6021 in slurry-state fermentation to produce pectinase with suitable enzyme composition for application in apple juice processing. The production of pectinase is improved by additional nitrogen source substances and mineral supplements. The ratio of carbon source substances to nitrogen source substances in the medium also has significant effect on the pectinase production by A. niger P-6021 in slurry-state fermentation. In the optimized medium composition, the maximal enzyme activity could reach 42 (UL-1)-L-. (polymethylgalacturonase), 6.7 (UL-1)-L-. (polymethygalacturatesterase), and 4.3 (UL-1)-L-. (polymethylgalacturonate lyase), respectively, after 3 days at 180 r(.)min(-1) and 30 degrees C. The crude pectinase shows significant effect to improve the yield and clarification of apple juice.