Steel-concrete composite structure has more and more been widely used in urban bridges,for it's advantage in reducing cross-section components' size, and ascendency in improving stiffness,stability and integrity of structures and ductility of components and structures,and it's predominance in shorten the construction period as well.Among all the steel and concrete composite structure styles,the combination of steel box girder with concrete deck is now very widely used.And this style is chosen in building the cloverleaf junction of Beijing South Railway Station.The important characteristic of cross-height ratio of curve-shaped steel-concrete composite structure is that it is related to the curvature,this paper made an optimizing analysis on this subject with one curve-shaped part of Beijing south railway station cloverleaf junction as model,and analyses the relation between cross-height ratio and curvature in terms of it's design with the help of general-purpose finite element software ANSYS.