Abstract: To study predation by Coccinella septempunctata adults on 4 stages of Poratrioza sinica Yang & Li, predation functional response, mutual interference, density influence and preference of C. septempunctata on P. sinica were investigated in laboratory and preying effect in field. The study indicated that functional response of adult C. septempunctata to P. sinica could be fitted by Holling Ⅱ model, the daily maximum numbers of P. sinica eggs, 1^st-2^nd instar nymphs, 3^rd-5^th instar nymphs and adults preyed theoretically by the adult C. septempunctata were 112.6, 536, 415 and 113.9, respectively. In 30 days of adult’s life cycle, density of P. sinica inside cages could be decreased by 80.1% in the field. Searching efficiency of C. septempunctata to P. sinica 1^st-2^nd instar nymphs was 0.9451 and processing time was 0.001865, which were better than those of other stages. The maximum rate of P. sinica 1^st-2^nd instar nymphs preyed was 80.2% as the prey density was 100 heads per dish, so the ratio of predator: prey was 1:100. The density had a greater impact than mutual interference on C. septempunctata. When different stages of P. sinica co-existed equally, C. septempunctata preferred P. sinica adult in 100 heads per dish while P. sinica nymphs in 300 heads per dish. The study showed that C. septempunctata has the potential to be predator of P. sinica and the newly-hatched nymphs could be controlled more effectively by C. septempunctata adult in field.