Abstract: Before the hardening of concrete core in construction of a Concrete Filled Steel Tubular (CFST) arch, the steel tubular rib will bear itself weight and the fresh concrete. Thus initial stresses will be built up in it. Total of 4 single circular CFST arch models with various initial stress degrees were tested; and parametric analyses by the finite element method of the influence of initial stress to the ultimate load-carrying capacities of such a structure were carried out. The results indicate that the initial stress will not influence the failure model but will make the ultimate load decrease. The influence of initial degree to the ultimate load of CFST arch has a strong relationship to arch slenderness and its rise-to-span ratio, but weak to load case. The ultimate load carrying capacity of a CFST single tubular arch with initial stress can be obtained by multiplying a reduction factor with the load carrying capacity of CFST arch without initial stress. The factor can be calculated by multiplying the two reduction factors, one related to slenderness and the other to rise-to-span ratio, whereas the can be attained by the revised equivalent beam-column method.