Abstract: To study the bond-slip mechanism of reactive powder concrete (RPC) filled in steel tubes, ten push-out tests were carried out on RPC filled in steel tube specimens. The failure patterns, load-slip curves and steel tube strains of specimens were analyzed. The effects of the length-diameter ratio, radius-thickness ratio and RPC strength on the bond strength are discussed. The results show that there is a sudden drop on the load-slip curves of specimens with small confinement coefficients, while the load capacity increases after the knee of the curves for specimens with large confinement coefficients. The bond strength basically increases with the decrease of the length-diameter ratio and the increase of the radius-thicknessratio. The effect of the RPC strength is not obvious. The steel tube begins to provide RPC confinement when the strain ratio ε_sh/ε_sv of steel tube is larger than its Poisson's ratio. The relationship between the internal pressure of the steel tube and the bond stress is established, and the calculation method of the interface bond strength of RPC confined by steel tubes is proposed based on the experimental results. The calculated results are in good agreement with those of the model test.