Abstract: The capacity of road network is a basic data in traffic field. Up to now, no method can compute truly the capacity of road network. Therefore, on the basis of reviewing the current theories and models for capacity of road network, considering the conception of capacity of road section, a new definition of the capacity of road network is put forward. The new definition is made of two parts, one is ideal capacity of road network, and the other is real capacity of road network. At the same time, the main factors influencing the capacity of road network are also identified, which lays a foundation for truly computing the capacity of road network.