Abstract: Numerical simulations of covered karst collapse commonly suffer from deficiencies such as fixed rock mass strength parameters and insufficient quantification of cave morphology effects, leading to a distorted representation of the progressive failure process. To address these issues, this study aims to reveal the progressive failure mechanism of karst collapse under rainfall infiltration and groundwater drawdown, and to quantify the controlling effect of cave morphology on collapse susceptibility. Using the soluble-rock area of Xianshui Lake in Pingshan, Shenzhen, as a case study, the built-in FISH scripting language in the FLAC numerical simulation platform was employed to dynamically degrade rock mass strength parameters, simulating the progressive failure process of tensile failure in the surrounding rock mass of karst caves. A comparative analysis was conducted on the collapse responses of a narrow elongated cave（2 m × 8 m）and an elliptical cave（6 m × 8 m） under vacuum suction erosion. The results are as follows: (1) Dynamic tracking of tensile failure units in the surrounding rock mass of karst caves was achieved, effectively resolving the challenge of depicting progressive failure in conventional fixed-parameter simulations;(2) The five-stage evolution mechanism of karst collapse under rainfall infiltration was revealed. Displacement field evolution analysis at 0.5 h, 0.75 h, and 1 h demonstrated abrupt instability characteristics during the late infiltration phase (1 h stage), with final collapse occurring through late-stage seepage; (3) The morphological effects of karst caves were quantified. The critical suction force (80 kPa) required to form a through-going plastic zone in the roof of elongated caves was only 50% of that for elliptical caves (160 kPa), indicating greater sensitivity to vacuum suction erosion; (4) The mechanical evolution chain was clarified: initial roof plastic failure → tensile crack propagation → vertical failure zone extension → soil plasticization development → full-section plastic zone penetration → collapse induced by sudden vertical displacement. An early-warning criterion based on roof displacement rate was established. This study provides theoretical support and technical reference for engineering geological surveys, disaster monitoring system optimization, and prevention engineering design in karst areas.