Abstract: The farming and pastoral interlock belt is situated in the northwest Hebei Province, which is a special agricultural ecozone. By means of black light lamp and diamondback moth sex pheromone luring and investigation, the population dynamics of phototactic insects in the farming and pastoral interlock belt of northwest Hebei Province have been studied for 82 days on end (from June 10th to August 30th in 2006). The results indicate that there are 269 kinds of insect species belonging to 9 orders, 42 families in this region. Four types of the population dynamics of phototactic insect species could be identified as sporadic appearance,successive appearance with small amount, successive appearance with great number and explode in a short-term. The dominant species of pests include Loxostege sticticalis Linnaeus, Plutella maculipennis Curtis, Ipimorpha subtusa Schiffermüller, Agrotis ypsilon Rottemberg, Scotogramma trifolii（Rottemberg）, Clostera curtuloides Erschoff. By analyzing the proportions of different groups and Seasonal dynamic of dominance species, some scientific material for the system of predicting pests and preventing pests has been basically provided.