Abstract: To clarify the control potential of Plexippus setipes on Ectropis grisescens, studies about the predator functional response, predation selectivity and intraspecific competition of P. setipes on E. grisescens larvae were conducted under indoor conditions. The results show that the P. setipes preferred to feed on the early stage larvae of the E. grisescens. There were significant differences in the predation ability among different developmental stages of P. setipes. Specifically, the adult spider had the strongest predation ability to hunt 17.44 larvae per day of the first instar of the E. grisescens, while the juvenile spider had relatively weak predation ability with only a daily of 2.33 larvae of the first instar. The predator functional response of P. setipes was in accordance with the Holling Ⅱ model. The Searching efficiency of P. setipes decreased with the increase of E. grisescens population. The predation selectivity shows that P. setipes showed positive preference (Ci > 0) for 1^st and 2^nd instar E. grisescens larvae along with negative preference (Ci < 0) for 3^rd instar larvae. The predatory effect of P. setipes on E. grisescens larvae was also influenced by their own population density. There was a strong intraspecific competition, which was consistent with the Hasse Ⅱ model. This study indicates that P. setipes had a strong predatory ability and control potential on E. grisescens larvae, providing a theoretical basis for exploring the use of spiders in tea plantations.