Mining-induced ground fissures can strongly intensify gully erosion. However, their quantitative effects and hydro-mechanical controls remain poorly understood. This study aims to elucidate how ground fissures alter gully headcut erosion under varying rainfall intensities and fissure configurations. To achieve this, laboratory rainfall experiments, UAV photogrammetry, hydro-mechanical monitoring, and CFD-based multiphase simulations were integrated using soils collected from the Wanli coalfield. The results indicate that rainfall intensity and fissure quantity synergistically amplified erosion. The maximum headcut retreat rate of 3.89 cm/min and sediment yield of 624.7 kg occurring under 90 mm/h rainfall with dual fissures. Gully erosion accounted for 75-89% of total sediment loss, whereas runoff decreased markedly in fissured scenarios, demonstrating that fissures intercepted surface flow and promoted preferential seepage. This seepage induced rapid increases in pore-water pressure, thereby reducing effective stress and accelerating collapse. Simulations reproduced the observed runoff and sediment responses well, with R2 values above 0.98. More importantly, ground fissures shifted the dominant erosion mode from gradual hydraulic scouring and niche development to abrupt episodic block collapse driven by preferential seepage and localized static-pressure gradients. Analyses of static pressure and pore water pressure indicated that the front of the fissures was subjected to preferential flow stress, which directly triggering the collapse of the headcuts and surrounding soil mass. These findings provide novel insights into the hydro-mechanical mechanism governing fissure-controlled soil erosion in mining-disturbed landscapes.