Abstract: In order to clarify the predation function and efficiency of Withius piger(Simon,1878) against stored grain pests and to evaluate the feasibility of application predatory natural enemies in the warehousing industry,the predation effect of W. piger on several stored product pests were studied by behavior observation and simulation function response. The results showed that W. piger could prey on 9 kinds of stored product insects,especially preference prey on Tribolium castaneum and Booklice. The poorest predatory effect was on Lasioderma serricorne Fabricius. The process of predation behavior W. piger on T.castaneum consisted of 5 steps:searching,catching(clamping prey),paralyzing,sucking body fluids and rest. The results of comparison predation number with difference stored product insects showed that the predation number against 3rd-instar larvae of T.castaneum was the highest with 19 individuals per day and the fewest predation number was 1.2 individuals per day against 3rd-instar larvae of L. serricorne. The predatory and searching efficiency of W. piger on the third-instar larvae of Liposceli bostrychophila was studied. The results showed that the predatory functional response of W. piger fitted better to Holling Equation II when the densities of L. bostrychophila were from 10 to 160 individuals. The maximum predatory amounts daily for L. bostrychophila was 78.7 individuals. The search area was 5.99 m². All the results indicated that W. piger had predation effect on several stored products insects and could be used as prey enemies to control the T. castaneum and booklice efficiently.