Abstract: Based on the random analysis of traffic demand and supply,the unblocked reliability of road is used to analyze the possibility of congestion happening.At the same time,the model of optimum route selection is provided,which is based on the analysis of unblocked reliability and the circuitous length as well as the historical data and experience.The results of this optimum route selection model can provide the route guidance information for the traveler,which can reduce the blindness of travel.