Ship motion,with six degrees of freedom,is a complex stochastic process. Sea wind and waves are the primary influencing factors. Prediction of ship motion is significant for ship navigation. To eliminate errors,a path prediction model incorporating ship pitching was developed using the Gray topological method,after analyzing ship pitching motions. With the help of simple introduction to Gray system theory,we selected a group of threshold values. Based on an analysis of ship pitch angle sequences over 40 second intervals,a Grey metabolism GM(1,1) model was established according to the time-series which every threshold corresponded to. Forecasting future ship motion with the GM (1,1) model allowed drawing of the forecast curve with effective forecasting points. The precision of the test results show that the model is accurate,and the forecast results are reliable.