Acidification processing of Engraulis japonicus oil's soapstock was optimized by Response surface methodology and fatty acid composition was analyzed in the study. Experimental results showed that optimal processing conditions were: H2SO44. 18 mL /100 g,reaction time 60 min,reaction temperature 71℃,ratio of material to liquid3∶ 7 /g∶ mL,and the conversion rate of soap was 99. 92%. There were 26 kinds of fatty acid in the crude oil with high acid value. The content of unsaturated fatty acids,saturated fatty acids,essential fatty acids,EPA and DHA were51. 69%,37. 18%,2. 78%,21. 89% respectively of the total fatty acids.