Abstract: Based on the natural population life tables of continuous two generations of the diamondback moth (DBM), Plutella xylostella L., the control effectiveness of Trichogramma confusum, Oomyzus sokolowsakii and Cotesia plutellae on DBM were simulated and evaluated by using state space equation and addition analysis method of population control. The results were as follows: in spring, any two species of parasitoids mentioned above could effectively control DBM population increase due to the strong natural control of parasitoids, while both T. confusum and O. sokolowsakii or three species of parasitoids released simultaneously could control the increase of DBM population effectively in autumn,because of the low natural parasitization of O. sokolowsakii and the high increase of population of DBM.