Percussion hammer drilling is a common method to solve the underwater reef-clearing task under ecological constraints.To improve the crushing efficiency of the reef without a free surface,this paper put forward the underwater shock hammer drilling technology combining drilling with impact hammers.Through the underwater drilling and impact hammer reef breaking field test,considering the water resistance effect of impact hammer movement in water and the cable drag effect,the impact hammer collision and penetration model under the influence of drilling is established.Combined with the 3DEC numerical simulation of drilling and impact hammer reef breaking,the damage evolution law of repeated impact of the hammer on the reef under the action of drilling is analyzed.The results show that drilling has no obvious effect on increasing the penetration depth of the underwater impact hammer,but the breaking depth and width of the reef can be significantly improved when the drop distance is below 10 m,and the reef cleaning efficiency can be increased by 183%.Hammer drop distance and drilling depth are the main controlling factors of reef-breaking efficiency.Under the combined action of drilling and impact hammer,the crushing volume after 5 shocks is about 103.24 times that of the first impact.Both drilling and multiple shocks can effectively improve the reef-clearing efficiency of the hammer,and drilling can further improve the reef-breaking efficiency of the hammer under multiple shocks.The research results can provide a reference for parameter design and site construction of underwater environmental protection reef clearing.