Wuhan Tianxingzhou Changjiang(WTC) Bridge and Nanjing Dashengguan Changjiang (NDC) Bridge are two super high-speed railway 3-trusses composite bridges.This is the first time of using three trusses in such large bridges in the world.These two types of railway floor systems of the two bridges have never been used in China before.The problem how to conform the deformations and stress levels of the railway floor system of WTC Bridge was studied.After finite element analysis and comparison,the plan ot arranging one expansion stringer every two panels in railway floor system were proposed and good effect was obtained.Because of the application of three trusses,the allocation of the loads acted on the deck in three trusses is different and varies in different places of NDC Bridge.This problem was studied by model experiment and 3D finite element analysis.The results of 3D FEM analysis coincide with the model test results.The allocation rule of the loads acting on the deck in three trusses was Presented.Because of the application of monolithic decks,the stiffness and structural integrity of NDC Bridge are high.