Abstract: The polyacylamide gel electrophoretic analysis was used to detect the changes of esterase isoenzymes (EST) in Pardosa astrigera (♀/♂) after feeding the beet armyworm Plutella maculipennis Curtis. The results show that the special EST of prey is found, the optimal detecting time for the polyacylamide gel electrophoretic is from 3h to 6h for the female spider and from 6h to 9h for the male spider after feeding. The female spider's digesting is quicker than that of the male.