The invention belongs to the field of road traffic application and in particular to a road traffic alarm predicting method. The method comprises the following steps of: acquiring traffic index characteristics in real time by supply devices; enabling the each group of acquired traffic index characteristics to correspond to road positions where the supply devices are located one to one; forming a group of characteristic vectors by the current acquired real-time traffic index characteristic values and a plurality of historical traffic index characteristic values; calculating pre-warning values describing the traffic states of the road positions according to characteristic vector fusion; adaptively selecting a threshold value; comparing the pre-warning values W(t) with the threshold value T, giving an early warning if W(t) > T, otherwise giving no warning. The method is simple and concise in calculation process and good in objectivity, and can predict and identify a decision whether to give a warning or not in time and accurately.