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Because the contradiction between hoisting weight and span of concrete filled steel tube (CFST) arch bridges was comparatively resolved, CFST arch bridges have become one of most rapid development bridge structures in last twenty years. To 2005, a CFST arch bridge with a span of 460 meters has been built. Furthermore, the span and amount of this type of bridge are still increasing. The building technology of CFST arch bridge in our country is at world lead level, however, the traditional design pursues the lowest lever rather than the best at the premiseof meetting standard. Especial for the design of more-limb-turss type arch rib, if we accord to the lowest lever, there will be not only a great wast of economy but also inconvenience in construction.The passage carry out research work based on under-construction Small River grand bridge (a six limbs deck arch bridge, clear span of 338m)1. Based on full stress optimize design theory, it set up the optimized objective function and constraints of CFST arch bridge cross-section;2. By using powerful finite element program, ANSYS, it set up Small Rive grand bridge arch cross-section optimization model to optimize the main arch, draw the corresponding optimal arch cross-section;3. Set up the optimal mathematical model of arch axis, calculated coordinate of all discrete point under the arch line closer to the coordinates of stress on a particular load;4. According to coordinates of Under the foot arch, 1/8, 1/4, 3/8 , use of the stress line cubic spline interpolation curve fitting function to draw sub-arch axis function, and use piecewise interpolation function to make comparative analysis;5. Use of ANSYS finite element program to compare strength, stiffness, stability before and after the model of optimization.
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