To investigate the influences of uncertainties on stable bearing capacity of CFST arches, the limit state function for lateral instability is established. The software ABAQUS is used to calculate the ultimate bearing capacity or critical load for stability with or without considering nonlinearities. Based on the FORM, the cooperative work of self programming with MATLAB and finite element software is adopted to obtain reliability and sensitivity indices for different initial loads. The results show that the real bearing capacities of CFST arches for lateral stability lie between critical load and ultimate bearing capacity, and the critical load is the upper limit. The geometric size has the most important influences on reliability index and it is followed by the elastic modulus and the material strength. The initial geometric imperfection has little effect within the limit of code. However, with the increasing of lateral load, the sensitivity indices of material strength increase, while the sensitivity indices of elastic modulus decrease.