As a key component of car collision-avoidance system, distance measurement puts emphasis on response time and accuracy. Several ranging methods applied in automobile area are discussed. In particular, machine vision is introduced as a popular way in distance measurement. To improve its response time and usability under bad weather, laser is adopted to locate obstacles. Experimental results show that the system can meet the ranging requirement of collision avoidance. Compared to traditional machine vision, the combined way can reduce 54% response time and 68% deviation.