<p>In this paper, enhanced near-field shock wave propagation in underwater explosion is achieved by introducing a fragile air-tube under the explosive. Firstly, based on the ALE algorithm in the ANSYS/LS-DYNA software, a numerical model integrating the water, the air, the explosive, and the air-tube is developed. Comparative discussion for explosion with air-tube in the air, as well as explosion in the water without air-tube, is made to highlight the distinct energy attenuation mechanism due to the introduction of the air-tube. Then, the influence of the tube geometry, as well as evolving structural boundaries, on the explosive process is discussed exhaustively. The results indicate that the air-tube acts as a shock focusing apparatus, significantly altering explosion flow dynamics. Tube damage mode relies on tube geometrical size. Time-refreshed structural boundary affects the position the fluid flowing into the air-tube, which in turn plays an impact on the bubble pattern and energy distribution near the tube outlet. Enhanced outlet pressure is strengthened along with the decrease of the outlet radius, cross-section height ratio and tube thickness. These insights offer valuable guidance for optimizing underwater explosion and possess prospectively scientific and practical significance.</p>