To study the rock-breaking efficiency of underwater rock drilling and blasting in Longxikou of the Minjiang River,we build a dynamic finite element model to compare the influences of the water-coupled and air-coupled medium on the blasting energy transmission efficiency.Meanwhile,we also analyze the dynamic response and energy characteristics of rock in open-pit and underwater blasting.The results indicate that the blasting energy and transmission efficiency transmitted into the rock in water-coupled powder charge conditions are greater than those in air-coupled powder charge conditions,which shows that a water-coupled medium can enhance the rock-breaking effect.In the water-coupled powder charge conditions,the water-covering conditions have no effect on the propagation of initial explosive stress waves.When the compressive stress wave is reflected from the free surface,the unit kinetic energy and internal energy of open-pit water-coupled blasting are relatively large.This indicates that the water medium in contact with the free surface in underwater blasting suppresses the rock mass movement and absorbs some of the blasting energy.Underwater blasting needs to increase the explosive unit consumption to obtain the same blasting effect as open-pit water coupling.