【Background】 Orius similis Zheng is a predatory natural enemy of many insect pests and has significant exploitation and utilization potential. There are, however, very few studies on its efficiency and control effects on the invasive insect pest, the western flower thrips, Frankliniella occidentalis (Perganda), thus limitings its use as a biological control agent. 【Method】 Prey preference, functional response and searching efficiency of O.similis adults on adults and nymphs of F.occidentalis in different experimental spatial arrangements were studied in the laboratory. 【Result】 Adults of O.similis preferred nymphs to adults of F.occidentalis. At the same experimental space, the number of daily prey consumption increased with increasing the prey density at 60 prey individuals per finger tube, the maximum consumption number of O.similis adult for the adult and nymph of F.occidentalis were 15.[KG-*8]9 adults and 19.[KG-*8]3 nymphs of the prey, respectively. However, the searching efficiency of O.similis adult decreased with increasing density of F.occidentalis. The functional response of O.similis adults could be described by a type Ⅱ Holling equation. The instantaneous attack rate of O.similis adult to nymphs of F.occidentalis was 1.[KG-*8]2794 in small rearing bottle, whereas the instantaneous attack rate of O.similis adult to adult of F.occidentalis is only 0.[KG-*8]3506 in large rearing bottle; the shortest time for a O.similis adult to treat with a F.occidentalis nymph is 0.[KG-*8]0242 d, whereas it need 0.[KG-*8]0402 d for treating with a F.occidentalis adult. In the same density of F.occidentalis, the average number of daily prey consumption of O.similis adults in large rearing bottle was lower than those in small rearing bottle. 【Conclusion and significance】 O.similis has strong prey efficiency on F.occidentalis and has control effect on the western flower thrips.This study aims to accumulate data for biological control of F.occidentalis, and laid a foundation for Integrated Pest Management of F.occidentalis.