Abstract: In order to know the parasitoidism of Arma chinensis on Spodoptera litura, the predation of 3-5 instar nymph and adult of A.chinensis on S. litura was studied in laboratory. Experimental data was fitted to the mathematical model HollingⅡ in which controlling effects were determined by parameters of preying potential capacity. The influences of the predator's density functional response were determined by the mathematical model Hassell. The results showed that 3-5 instar nymph and adult predators exhibited Holling II functional responses, with the order of attacking efficiency being 3rd (1.873) > female (1.329) > 4th(1.187) > 5th(1.125) > male(0.828). The maximum daily predation number of female was 13.699. With the increase of prey's density, predators' searching effect decreases gradually, and the searching effect of female was obviously larger than that of other stages. As the density of A. chinensiss increased, the interference was stronger and the average predation decreased. It indicated that female A. chinensis has a greater predation potential for S. litura.