In this study a four-leg lattice structure CFST arch bridge is analyzed using finite element software (ANSYS) to predict the ultimate bearing capacity considering several parameters (slenderness ratio, steel content, steel type, and concrete type) under two influencing factors initial stress and geometric defects. There is an inverse relation found between the existence of the initial stress and ultimate bearing capacity and ultimately the overall stiffness of the structure has been reduced during non-linear stage. Larger the slenderness ratio, the greater the influence on the ultimate stability bearing capacity of with initial stresses and geometric defects. According to the ultimate bearing capacity coefficient under different steel content ratios, it can be known that the greater the steel content higher the bearing capacity coefficient. The increment rate of the ultimate bearing capacity coefficient is between 0 and 18%. The comparison of the ultimate bearing capacity coefficients under the four steel types shows that compared with Q235, the other three steel types the ultimate bearing capacity coefficient is 12%-24%.However, there relatively small influence of the two concrete grades C60 and C55 on the ultimate bearing capacity of the CFST arch bridge. The effect of initial defects in in-plane as better than the initial defects out-of-plan on ultimate bearing capacity CFST arch bridge. A comprehensive consideration of influence of the initial stress and the initial out-of-plane defects are considered simultaneously. The analysis results show that the amplitude of geometric defects is controlled within L/5000, and the initial stress is controlled within 0.4 within a reasonable range.