It is estimated that there are nearly 20 million hectares of rice crop being infested by Nilaparvata lugens, with an annual loss of some half a million tones of grain. In order to study the properties and laws of Nilaparvata lugens occurrence system further, the time series data of Nilaparvata lugens occurrence from 1986 to 1998 collected in Taihu Lake District were analyzed by using the methods of autocorrelation function, power spectrum figure, phase trajectory figure, poincare section, and return map of chaos theory. The results indicated that Nilaparvata lugens occurrence system in Yangtze River valley area in China had an obvious chaotic property, even though there was some interference of random noises.