Abstract: Theoretical method of establishing the relationship between the volume of transit-rider and its trip (time) cost, the so-called cost-function of transit route flow, is proposed in this paper. Based on analysis of characteristics of mixed traffic flow and trip characteristics of passengers, the value of coefficient in the formula of transit route cost-function which is derived from the theory of traffic flow can be calculated with the data gained from field surveys on main lines of buses within the transit networl specified for study.