Abstract: This paper conducted underwater contact explosion tests on concrete-filled double-skin steel tube (CFDST) columns.The CFDST column used in the test was cast on site,with a height of 1 m.The outer diameter of the outer steel tube was 325mm,the outer diameter of the inner steel tube was 159mm,and the thickness of both the inner and outer steel pipes was 6mm.Through the explosion tests,the damage modes of CFDST columns under underwater contact explosion were preliminarily explored.By using finite element software,a coupling model of CFDST columns under underwater contact explosion was established,and the reliability and validity of the coupling model were verified by comparing with the test results.On this basis,the dynamic response characteristics and damage evolution laws of CFDST columns under underwater contact explosion were further explored,and the influence of the hollow ratio and concrete strength on the damage modes of CFDST columns was analyzed.The results show that CFDST columns exhibit significant local denting damage characteristics under underwater contact explosion,with both the inner and outer steel tubes denting inward.The internal concrete damage is most severe in the area near the explosion center,but the column body does not undergo overall deformation.As the hollow ratio increases,the denting area and deformation of the outer steel tube increase.Compared with a hollow ratio of 23%,when the hollow ratios are 33%,50%,and 67%,the denting deformation of the outer steel tube increases by 2.5%,14.5%,and 117.6% respectively,and the denting area increases by 36.1%,124.2%,and 459.7% respectively.The increase in concrete strength can effectively reduce the denting area and deformation of the outer steel tube.Compared with C40 concrete,when the concrete strength is C60,and C80,the denting deformation of the outer steel tube decreases by 6.5% and 13.4% respectively,and the denting area decreases by 33.8% and 67.3% respectively.