The invention discloses a macroscopic fundamental diagram-based road network key section identification method. The method comprises the steps of 1, acquiring the traffic flow, the average speed and the time occupancy data of each road section of an urban road network A; 2, calculating a weighted flow and a non-weighted density of the road network within each acquisition period; 3, getting a set of samples; 4, drawing a macroscopic fundamental scatter diagram; 5, calculating the critical weighted traffic flow of the road network MFD; 6, arbitrarily deleting one road section, and calculating the critical weighted traffic flow of the road network (-i)MFD without the above deleted road section and the floating value of the MFD critical weighted traffic flow of the road network A; 7, adopting the clustering analysis method for classification, and extracting a threshold r and a key road section. According to the technical scheme of the invention, the defect that the key section identification result based on the static topology structure of the road network is not consistent with the dynamic characteristics of the road network traffic flow can be overcome. Therefore, the method is more applicable to the change characteristics of the road network traffic flow. Therefore, the reliability of calculated data is ensured to be high.