Abstract: The key to ambiguity toll distribution for expressway is to judge the matching states and use the scientific distribution method. This paper studied the differentiation of matching sample by using K-Nearest Neighbor( KNN) theory,and put forward the algorithm of ambiguous toll distribution based on KNN and license plate recognition technology. Taking the ambiguity of Beijing-Shanghai expressway and Tianjin-Changzhou expressway as an example,this paper proved that the discriminant effect of KNN is better than RBF neural network and BP neural network by experiments,and then proved that the distribution method for ambiguous toll of expressway based on KNN is fairer and more objective.