A coral sand cement mortar was prepared with 2.0% SiO2 nanoparticles, 0.4% basalt fiber and artificial seawater. The impact compression strength of the samples at different confining pressures (i.e., 0-20 MPa) was determined by using a split Hopkinson pressure bar with an active confining pressure device. The dynamic mechanical properties of SiO2 nanoparticles reinforced coral sand cement mortar were analyzed at different confining pressures and strain rates. The results show that the failure pattern of unconfined (uniaxial impact) specimens occurs, indicating the brittle characteristics. The better integrity of the specimen after being impacted appears under the active confinement, which belongs to a compressive-shear failure. Moreover, the specimen undergoes a transition from brittle to plastic, thus improving the toughness. From the obtained dynamic stress-strain curve, the strength of the specimen is increased by 2.08-3.43 times, compared to that under static conditions, and the dynamic compressive strength is 1.88-2.35 times greater than that of unconfined (uniaxial impact) specimens. The relevant empirical formulas were obtained via analyzing the dynamic increase factor and confinement increase factor of the material and their corresponding effects on strain rate and confining pressure variation. At the same confining pressure, the specific energy absorption of materials shows a linear increase with the incident wave energy. Through the analysis of energy dissipation, the confining pressure can increase the specific energy absorption value of SiO2 nanoparticles reinforced coral cement mortar.