This paper reports on experiments involving deep underwater explosion (UNDEX) that were conducted in a pressure container. The bubble pulsation behavior due to the deep UNDEX is recorded by a high-speed camera for equivalent depths up to 350 m. The bubble images show that although the shape of the explosive package affects the bubble shape at the initial moment, the bubble easily becomes spherical in shallow water which is 0.8m and 100m depth, but never becomes spherical during the whole first pulsation in deep water which is 200m, 300m and 350m in this paper. Solutions of the Rayleigh–Plesset equation fit well with the experimental data, and the value of the polytropic index γ of the gaseous detonation products changes from 1.25 to 1.3 as the depth is increased. Finally, empirical laws governing the pulsation of a deep-UNDEX bubble are established. The experimental pulsation period and that from the Rayleigh–Plesset equation agree with that obtained empirically, but the maximum radius is smaller than the empirical one. This phenomenon shows that the water depth not only creates a high hydrostatic pressure for the bubble but also changes the energy-release process of a deep UNDEX.