Taking underwater reef blasting in Gulei sea channel of Xiamen Port as an example, the forming characteristic of shock wave in water for underwater drilling blasting is analyzed. By field monitoring, the pressure of shock in water for different distances is attained, the major parameter, such as pressure amplitude and positive action time, and the propagation attenuation rule of shock in water are researched in this paper. The result can helpful for engineering design and construction and environmental safety assessment.