The experiments will add three kinds of n-6 polyunsaturated fatty acid --Linoleic acid,γ-Linolenic acid and Arachidonic acid in different amounts from 0.5% to 3% to feedsfor rearing grass shrimp.During rearing perids, it will determine the average bodyweight , survival rate and feed efficiency in every 15 days of each ponds. Analyze fattyacid of shrimp muscles and feeds . IT also will analyze the Hemocyte and Bacteria ofshrimp and in attack experiment. So it will enhance shrimp disease resistence andincrease farmers economic profits.