To satisfy rigid performance specifications of real-time and accuracy while tracking and locating mouth region in an intelligent driver assistance system, a new method is proposed. The idea is implemented with two steps, tracking and target detection. In the tracking part, by making a diffusion of tracking range, and optimize process of update learning factor to achieve long time tracking; In detection and positioning section, fully taking the difference of each human mouth and different expressions into account, the accuracy required in the auxiliary driving system is achieved by use of Adaboost algorithm. In addition, through the introduction of compressed sensing and cascade classifier, rapidness is also guaranteed. Experimental results show that the method can reach the target while it is applied in driver assistance system. It is a strong significance of practical application.