Abstract: Explosive welding is an advanced technology to achieve metallurgical bonding of dissimilar materials.Stand-off distance has a great effect on bonding quality.A 3D finite element model of explosive welding of steel/copper/copper three-layer tubes was established on the platform of ANSYS/LS-DYNA.The effects of stand-off distance on the explosive welding process and bonding quality were studied.The simulation results indicate that high bonding quality can be achieved when stand-off distance 1 and 2 is set to be 1/4-1 times of the thickness of flyer tube 1 and 1/2-2 times of the thickness of flyer tube 2 respectively.They do a little effect on the maximal plastic strain and the maximal effective stress of the bonded tube, which increase rapidly within 6 μs and then are stable.Stand-off distance 1 effects the movement of flyer tube 1 and flyer tube 2, while stand-off distance 2 only effects the movement of flyer tube 2.