Abstract: The reaction function of the second system has been derived from the equations of differentiation and systematic state-space expression when the roots of the property equation are two conjugate complex ones. The results obtained from these two methods are identical. Based on the data of tea leaves yield (1959~1973) in Chuanbu Tea Plantation in Yixing, Jiangsu, grey model (1,1) and grey model (2,1) have been built to predict tea leaves yield since 1973. Results show that GM (1,1) is higher than GM (2,1) in precision of prediction.