How to quantify the macro capacity of an urban road network is a new approach to studying urban total road network capacity in the recent years. A French scholar Mason (1989) has provided the magnitudes of time and space usage of city road network occupied by traffic bodies. This theory simply shows the inner effectiveness of various traffic models in terms of traffic bodies occupation of time of road network space or of space of road network time in the form of quantity, as well as investigates in convenience the intrinsic potentials of ur-ban road traffic infrastructures (inclusive of static and dynamic ones), for example parkingmotoarway. bikewary, pedestrian and etc. On the other side, it can further prove and compute the urgent economic costs of time and space usage of road net, and its economic revenues produced by that usage. This paper amends the concept of time and space usage of road net on the basis of Mason's, especially taking the density of urban road network into the consideration, and it mostly represents the reality. Although the model is a little bit compli-cated, it can be more effective if the methods pevided by ths paper are used. This can be verified by the case study of Zhuzhou City, Hunan province. Ths paper uses Zhuzhou data giv-en in 1990 as a pilot study city. All the pocess and results have shown that the ways given in the paper are useful, rational and efficient.