Road boundaries detection and tracing is a key technique for predicting warning system of vehicle based on the computer vision. With the selected road model, for the road without middle line, the road recognition algorithm is composed of two modules. The road boundaries detection module is used to get the information about road boundaries when vehicle just runs. Meanwhile the boundaries following module is started to predict the position of road edge when vehicle runs stably with the prediction knowledge. The road boundaries detection module amalgamates two kinds of information together and uses the adjacency of them in the space to get the exact information of road boundaries. The arithmetic is effective and precise.