Based on Hidden Markov Model, a new prediction method on driving status is advanced. In which, the velocity of following car, the velocity difference and distance headway is input as observation variables, the driving status is output as hidden variable. First the probability of observation status needed is calculated by forward algorithm, then the probability of observation status and driving status appeared together is calculated, at last, the prediction value of driving status could be got by conditional probability. The warning character of the prediction method could be evaluated not only by the accuracy but also by a new index [delta]ATp, which could show the degree of warning time at p probability. The results of simulation show that the method is right, which is in agreement with the result of eye movement checking method named PERCLOS, and it could complete the predictionprediction: when P%= 30%, �[delta]ATp = 2min7 sec, when P%= 40%,[delta]ATp = 1min51 sec; when; when P%= 50%, �[delta]ATp = 56 sec, when P%= 60%, [delta]ATp = 34 sec.