Abstract: The segmentally assembled structure of shield tunnels inherently results in numerous joints, representing potential leakage points. During leakage disaster development, the leakage zone is highly susceptible to progressive evolution, characterized by the continuous emergence of new leakage points. To investigate the influence mechanism of this progressive leakage point evolution on soil erosion patterns, a visualization-capable soil erosion test apparatus is designed to simulate the progressive process. Initially, comparative tests are conducted with and without contact pressure applied between the soil particles and the model box cover plate (analogous to the tunnel bottom lining). These tests reveal the dual mechanism of contact pressure on soil erosion: (1) Contact pressure enhances inter-particle interaction forces, leading to increased movement correlation among adjacent particles and consequently an enlarged erosion area; (2) Conversely, contact pressure increases frictional resistance, thereby suppressing the maximum erosion radius within the erosion zone. Subsequently, two-point progressive leakage tests are performed. These tests elucidate the mechanism of accelerated erosion deterioration: although the activation of the second leakage point does not establish a new independent erosion channel, it significantly widens and extends the pre-existing channel. Finally, comparative tests with both leakage points simultaneously active further demonstrate that, compared to scenarios where leakage points are activated concurrently, progressive activation induces a larger erosion region. This is attributed to the progressive disturbance imposed on the soil specimen during sequential activation. These findings highlight the necessity of considering the progressive evolution of leakage points in studies of tunnel leakage disaster mechanisms. The results provide a valuable theoretical foundation for understanding and predicting the progressive leakage disaster mechanism in shield tunnels.