Abstract：Research purposes： With the road - culvert transition section of Beijing - Shanghai high - speed railway Langang section CRTS Ⅱ type slab track as the background，by numerical analysis software Abaqus the coupling model of vehicle - track - transition section is established，the different factors to the safety and comfort of road - culvert transition section are studied. According to the range analysis and variance analysis method，the importance order of the factors affecting the train running safety and comfort is determined， the design of optimal transition section is put forward. Research conclusions：(1) With the maximum absolute value or the line lateral stability coefficient for optimization of test index，the way of transition section is the first influence factor； With wheel derailment coefficient，reducing load rate，and Sperling comfort as the test index optimization， driving speed is the first influence factor； With vertical acceleration as the test index optimization，filling thickness is the first factor. ( 2 ) It is recommended that in the design of road - culvert transition section adopting the scheme of inverted trapezoidal transition， transition section length 25 m， span length 2 m，filling thickness 4 m and speed 330 km/h，can make the train running safety and comfort and achieve optimal state. ( 3 ) The research results can provide a reference for the design of the other high - speed rail road culvert transition section.