Forward collision warning/collision avoidance (FCW/CA) systems have been developed to reduce rear-end crashes. Deceleration of vehicle is always defined as a default value in many typical proposed FCW algorithms. Considering the braking acceleration is always changed when the vehicle is braking, this paper analyzed the five typical FCW algorithms and proposed a new FCW algorithm based on road friction. The model described vehicle deceleration variation during the braking process, which was used to set up an FCW algorithm based on road friction considering the lead vehicle in three different kinematic scenarios: stationary, constant motion, and decelerating. Finally, the five typical FCW algorithms and the proposed algorithm were compared by simulation experiments. The effectiveness of the proposed warning algorithm was verified. It was concluded that the proposed algorithm was effective and conformed to the actual situation than the five FCW algorithms. Limitations and further studying recommendations for expansion of the paper were provided at the end of the paper.