The invention discloses a staged construction method of a multi-bridge-floor-layer suspension bridge for a highway and a rail. The suspension bridge is a three-bridge-floor-layer suspension bridge composed of a double-layer parallel main truss structure, rail transit is located on the uppermost layer, and highway traffic is located on the middle layer and the lower layer. The staged construction method of firstly constructing the highway traffic and then constructing the rail transit is adopted, construction on the rail transit can be carried out in the running process of the highway traffic, the scheme of the three-bridge-floor-layer suspension bridge is adopted, structural efficiency can be improved, the adaptive capacity of the structure on terrain is enhanced, the structure can adapt to the requirement for staged construction of the rail transit and the highway traffic, the recent engineering construction investment is effectively reduced, idle resources are avoided, meanwhile, the requirement that existing traffic circulation is not interrupted in the long-term construction period can be met, and the influence of construction on traffic is reduced to the largest extent.