Abstract: This study addresses severe floor heave in flexible formwork gob-side entry retaining under complex geological conditions. The 42305-working face of Wanli No.1 Coal Mine is selected as the engineering background. XRD and SEM tests are used to analyze the mineral composition and microstructure of floor sandy mudstone. Based on slip line field theory, the formation mechanism of floor heave is revealed. The test results indicate that the roadway floor contains abundant hydrophilic minerals (e.g., kaolinite). Water absorption causes lithological deterioration and particle disintegration, sharply reducing cohesion and shear strength. This phenomenon constitutes the internal cause of floor heave. Overlying strata loads are transferred to the floor via the coal rib and flexible formwork wall, forming an asymmetric plastic failure zone. The failure depth on the coal rib side reaches 2.0 m, much larger than the 0.6 m on the wall side. The inclination of the flexible formwork wall further induces lateral extrusion, leading to asymmetric squeezing floor heave. Based on engineering practice, an asymmetric floor control technology combining shallow-hole pipe concrete piles and deep-hole split-set bolts is proposed, with the dip angle of flexible formwork support bodies optimized. Field monitoring shows that the floor heave is controlled within 55 mm and the surrounding rock deformation is stable. This study provides technical references for similar projects.