Abstract: The demand for big-medium-sized tractors in China is a complicated non-linear system. Under the analysis of the characteristics of agricultural equipment demand system, a model of the demanding characteristics analysis and the research of predicting time-scale based on chaos theory were constructed. The paper focused on phase space reconstruction, correlation and Kolmogorov-sinaientropy applying the actual data of the domestic demand for big-medium-sized tractors from 1952～2004. The result showed that demand of agricultural equipment was chaos system, which indicated that there should have about 1～12 independent variables for describing demand change characteristics and the forecasting time-scale is about eight years.