In order to evaluate the operation status of urban traffic network dynamically, based on the two-fluid theory, the two-fluid service level parameter n is deduced and analyzed by introducing traffic flow theory and lo- gistic growth model. It is found that the value of n is not unique because the influence of network speed distri- bution is not taken into account, so the operation status of the network could not be evaluated well and accurate- ly. Based on the basic assumption of the two-fluid theory and the dynamic OD matrix, a new real-time dynamic evaluation method is proposed, which takes the parking time ratio f_s as the index. The simulation results show that this method can avoid the shortcomings of the two-fluid theory in evaluating the road network with parame- ter n, and better evaluate the real-time operation status of the road network. The operation status of the network is better as the ratio f_s decreases. The validity of the evaluation method is verified by an example of Nanjing road network of trunk line.