Abstract: Objectives Deep-sea pressure hulls face implosion risks when bearing extreme hydrostatic pressures exceeding their ultimate bearing capacities. Therefore, it is necessary to investigate the failure mechanism and shock response characteristics of the titanium alloy cylindrical shell implosion. Methods Firstly, an independent deep-sea implosion experiment platform was constructed, and the underwater experiment of the titanium alloy cylindrical shell was conducted in a deep-sea high-pressure environment. Then, the compressible multiphase flow module is developed to solve the high-speed motion of the flow field in the underwater implosion. The explicit nonlinear finite element method is utilized to analyze the dynamic response of the collapse and failure of titanium alloy cylindrical shells. Finally, the characteristics of the titanium alloy cylindrical shell implosion are examined, including the mechanism of fluid-structure interaction, the evolution law of asymmetric shock wave in the multiphase medium, the nonlinear dynamic response of the structure, and the energy balance relationship. Results The result found that the titanium alloy cylindrical shell with a length-to-diameter ratio of 2 collapsed in the form of first-order instability mode, and the implosion center formed twice successively. With increasing hydrostatic pressure, a pronounced migration effect of the first implosion center was observed. Meanwhile, the failure mechanism of the titanium alloy cylindrical shell transitions progressively from inward extrusion to inward curling, while the rupture morphology evolves from an arcuate shape to an m-shaped configuration. Conclusions This study reveals the failure mechanism and shock response characteristics of the titanium alloy cylindrical shell implosion, which has positive guiding significance for the implosion assessment and protection research of deep-sea pressure hulls.