The coexistence and dynamic development of multi-state traffic flow in mass fog bridge area lead to drastic change of vertical action density and dynamic application of longitudinal force. In order to analyze the structure effect in the fog environment, two key problems need to be solved, which are the development of the simulation vehicle flow under the mass fog and the improvement of the vehicle bridge coupling mechanical relationship. Firstly, the fog boundary was vertical, and the actual mass fog was abstracted as the mass fog box. According to the popular characteristics of mass fog vehicles, the mass fog bridge area was continuously divided, and the calculation method of vehicle flow characteristic parameters of each bridge section was deduced and determined, forming the development model of vehicle flow under the condition of mass fog, solved the establishment of multi-stage speed change points in the traffic flow model with the method of group mass fog identification. The simulation program was compiled and connected. Secondly, The state of motion in which a vehicle decelerates first, then moves at a constant speed and finally accelerates in mass fog, it broke through the general rule of once constant speed change of macro traffic flow and need to match the mechanical model of vehicle transmission and integrate into the vehicle bridge coupling system to construct the response analysis platform of vehicle bridge system under the condition of mass fog. Finally, Taking a typical cable-stayed bridge as the background, the influence factors and analysis indexes of the bridge response to the mass fog were calculated and determined, and the parameter analysis of the influence of the fog range and location factors on the bridge response was carried out. The results show that the displacement along the bridge and the vertical displacement of the bridge under the condition of mass fog exceed the condition of the same ownership and the standard traffic flow, the maximum value appears as the mass fog in the middle of the span, the uneven distribution of vehicle load and the longitudinal force caused by mass fog on the bridge cannot be ignored; as the mass fog range is constant, with the mass fog moving to both ends of the bridge, the influence of the mass fog on the longitudinal and vertical displacement response of the bridge decreases gradually; as the mass fog center is fixed in the middle of the bridge, with the mass fog range increasing, the displacement of the beam along the bridge increases first and then decreases, and the vertical displacement decreases gradually and approaches to 1.