With the rapid development of subsea tunnel projects worldwide, accurately assessing the stability of tunnel working faces intersected by jointed rock masses has become a critical engineering concern. This study aims to investigate the stability and failure characteristics of subsea tunnel working faces considering the influence of geological joints, drawing upon the Qingdao Guoxin Second Jiaozhou Bay Subsea Tunnel as a practical reference. Numerical simulations based on the Material Point Method (MPM) are systematically performed to analyze the progressive failure mechanisms and collapse evolution processes in jointed rock masses. Various numerical scenarios incorporating different tunnel geometries, internal friction angles, cohesive strengths, and rock joint mechanical properties are established to explore their impacts on face stability. The simulation results indicate that geological joints markedly decrease the stability of the surrounding rock, with both joint orientation and filling material significantly influencing failure initiation and propagation. Additionally, the mechanical properties of intact rock and filled joints have comparably critical effects on the excavation stability. The insights obtained highlight key controlling factors and failure patterns, providing essential guidance for risk assessment and stability control in subsea tunnel excavation.