A field plot experiment was conducted to study the community structure and species diversity of major predatory natural enemies in a rice-duck integrated farming system across rice growth season. Three treatments were installed, namely, rice-duck farming, conventional rice farming, and the control. The dominant species of major predatory natural enemies in the three treatments were all of Araneidae, Erigonidae, Lycosldae and Tetragnathidae. The dominance indices of Araneidae, Erigonidae and Lycosldae in the rice-duck farming were higher than those in the other two treatments. During the rice growing season, the total number of the major predatory natural enemies in the rice-duck farming and conventional rice farming were 14.9% and 1.7% lower than that in the control, respectively, and except in individual observation periods, the diversity index of the main predatory arthropods in the rice-duck farming was lower than those in the other two treatments. The decline of the diversity index of predatory natural enemies was more noticeable at the early stage after the introduction of ducklings into the experimental plot. With the growth of rice, the diversity index of major predatory natural enemies in the rice-duck farming showed a persistent increasing trend.