Generally, the planning of highway is designed on the basis of the traffic volume prediction. Because the influence factors of the traffic volume prediction are indeterminate, it leads to great discrepancy between the traffic prediction and the actual volume. Grey-markov forecasting model was founded by applying the model of GM (1,1) and Markov random process theory. The model utilizes the advantages of Grey-markov GM (1,1) forecasting model and Markov random process in order to discover the developing and varying tendency of the forecasting data sequences. When Markov random process is being used to decide the transfer rule of the state, it can not only make full use of the information of the historical data, but also improve the forecasting accuracy of random series. So it develops the applying range of grey forecasting and presents a new method of data sequences with large random. The analysis of an example indicates that the grey-markov model has good forecasting accuracy and excellent applicability.