A series of laboratory experiments have been performed to study the enhanced coupling of explosions by placing them in water-filled cavities or in air-filled cavities on a half sphere apparatus of cement mortar with 1.6 m in diameter. There is a cavity of 0.3 m in diameter at the center of the apparatus, the cavity can be filled with water or inserted a core of cement mortar, the source conditions consisted of tamped source and spherical cavities with a spherical charge of yield equivalent to 1.00 g of TNT. Measurements consisted of longitudinal strains of the aluminum bars sticking on the surface of the sphere apparatus at several points, and from which particle velocities, displacements were obtained. On the basis of the results of these small-scale experiments, conclusions are drawn concerning the coupling of the explosive energy. The effect of cavity decoupling in water is not as good as in cement mortar. When the explosive source is detonated in a water-filled cavity, the stress wave coupled into cement mortar is greatly enhanced. It follows that the damage of surrounding rock or dam by underwater explosion would be more possibly compared to the explosion detonated in themselves with same yield and same distance, and the enhanced coupling seems to be shown for air explosion nearby water.