Concrete-filled galvanized corrugated steel tubular (CFGCST) column is potentially an economic member to overcome the corrosion of outdoor structures, of which the anticorrosive corrugated steel pipe (CSP) can be used conveniently as the corrosion protection and permanent concrete formwork. The confinement effect provided by CSP essentially contributes to the structural advantages of CFGCST, whilst it, brings about complexities in corresponding load-resisting mechanism. Apart from the non-uniform distribution of stresses of CSP through thickness and height due to its curved shape, the confinement also varies across cross-sectional depth due to eccentric compression. The in-depth understanding and accurate quantification of the confinement effect of such member become a key issue that needs to be addressed. To investigate the impact of confinement on cross-sectional behavior, 24 specimens were tested with 5 load eccentricity ratios and 2 confinement factors. The non-uniformities of confinement along with height and cross-sectional depth were studied based on finite element modelling, validated via measured strains and load bearing capacities. A theoretical derivation was then conducted to characterize the non-uniform confining stress by fully considering the bidirectional curvatures of CSP, as well as the influence of debonding failure on the confinement. In each period of corrugation, the calculation method of equivalent confining stress was proposed based on the uniformization of stresses and geometry.