This paper presents a numerical model based on fiber element formulations for simulating the nonlinear inelastic behavior of eccentrically loaded circular concrete-filled steel tubular (CFST) slender beam-columns with preload effects. Deflections caused by preloads are included in the global analysis of CFST slender beam-columns as initial geometric imperfections. Computational algorithms based on the Müller's method are developed to obtain load-deflection responses of CFST slender beam-columns including preload effects. The accuracy of the numerical model is examined by comparisons of computer solutions with experimental results. The numerical model is utilized to investigate the effects of preloads on the axial load-deflection curves, column strength curves and ultimate strengths of circular CFST slender beam-columns under eccentric loading. The numerical model is shown to be accurate and efficient for predicting the behavior of circular CFST slender beam-columns with preload effects. The results obtained indicate that the preload with a ratio of 0.8 might reduce the ultimate axial strength of the CFST slender beam-column by 17.4 %.