Abstract: The rest in the traditional citrus fruit processing a large number of citrus peel is often thrown away, not only polluting the environment but also wasteful.Using the cellulose and pectin in citrus peel as fermentation substrate to produce Single Cell Protein, in order to promote key amino acids (threonine, methionine, lysine) yield and absorption efficiency, was very meaningful. After single factor study on product, threonine, methionine, lysine was 2.03×10-3, 3.58, 1.49×10-2g/L respectively, and the total key amino acids yields account for 14.77%of total amino acids, the optimized culture was 60g/L citrus peel, 21g/L urea, inoculum size of 20% (V/V) of the mixed bacteria (Aspergillus niger∶Saccharomyces cerevisiae=1∶1) , the optimal fermentation time was 5 days.