To study the complex mechanical movement and accumulation process of broken blocks in the process of underwater rock bench blasting,a fluid-solid coupling numerical calculation method based on FLUENT-EDEM was adopted.Firstly,the parallel bond and Hertz-Mindlin contact model were introduced between the particles,and the parameters of the parallel bond were calibrated by comparing the results of Brazilian splitting experiment and numerical calculation.Furthermore,the underwater bench blasting model was established,and the mechanical action mechanism of water on rock mass breaking and movement was analyzed.Finally,the whole ejection process of particles from a submerged step block was studied,and characteristics of the block velocity,block stacking and flow field were discussed.The results show that the accumulation and stratification of block particles are related to their initial velocity and height,and the horizontal movement distance of the block particles in the middle step is the biggest under the explosion load action.Meanwhile,the block particles in the upper blocking part mainly roll and cover the middle block particle layer under the action of gravity and buoyancy,which are less affected by the explosion load.Additionally,the explosion energy is mainly used to break the rock at the initial detonation stage,and the water has no obvious flow velocity.With the bulging and throwing movement of block particles,the fluid streamline velocity near the front surface of the bench is largest.When the block particles start to roll and slide,the streamline is mainly affected by the movement form of the particles.Therefore,the fluid-solid coupling model by Fluent-EDEM can accurately simulate the block motion in the underwater bench blasting,which can provide a new research method for underwater rock blasting engineering.