With the increase of span length of steel box truss arch bridge, the problem of nonlinear effect becomes even more promient. The ultimate bearing capacity is an important means of evaluate the performance of bridge safety.So it is significant important in the practical engineering to study the ultimate bearing capacity of long span half through steel box truss arch bridge. A Yangtze River Highway Brige is a long span half through steel box truss arch bridge with a main span 519 m. The ultimate bearing capacity of the structure are analyzed using the spatial finite element model. The results show that the influence of nonlinearities must be considered in the analysis of ultimate bearing capacity.