Highway features high levels of energy consumption and carbon emission. Developing a novel highway energy system with self-consistent energy supply becomes significant approaches for realizing carbon peak and neutrality in China. However, the spatio-temporal random distribution of traffic loads and the uncertainty in users’ charging decisions pose challenges to the supply-demand balance of highway electric-transportation coupled systems. To solve this problem, the “telegraph equation” of traffic flow based on fluid mechanics and electromagnetic field theory is proposed, which describes the spatial-temporal propagation mechanism of traffic energy flow and overcomes the defect that the traditional analysis methods can not reflect the mobility of electric vehicles. To simplify the calculation, a traffic energy circuit is constructed based on the methodology of the deduction from “field” to “circuit” in the electric circuit theory, and proposes traffic network elements such as resistance, inductor, capacitor and so on. Traffic energy flow theory of highway lays a theoretical foundation for self-consistent research of transportation-energy system.