Abstract: Rational slope stability-controlled mining method can effectively ensure the safety and stability of open-pit mine slopes, facilitate seamless production capacity transition, and enhance the economic benefits of mining areas. The Baiyinhua No. 1 Open-pit Coal Mine is a typical soft rock open-pit mine with developed weak interlayers, featuring four main minable coal seams. Affected by the deformation zone in the northeastern slope of the mining area, 53 million tons of resources were encumbered, making the originally designed vertical mining plan difficult to implement and severely impacting the mine's economic efficiency. Simultaneously, influenced by the advanced internal dumping of the Baiyinhua No. 2 Open-pit Coal Mine and the northern external waste dump, safety hazards existed in the eastern and northeastern slopes of the mining area. To reduce resource waste and ensure the safe, economical, and efficient operation of the Baiyinhua No. 1 Open-pit Coal Mine, a slope stability-controlled mining method termed "layered backfilling with intensified internal dumping" was proposed. The study adopted a change in the mining procedure, switching the coal working line to a transverse mining method to mining the deformation zone. Part of the deep coal seam was reserved as a supporting and retaining coal pillar. This enabled advanced internal dumping to backfill and stabilize the eastern and northeastern soft rock slopes. A mathematical model for optimizing the coal pillar was established. The calculated geometric parameters of the reserved pillar are: an upper southern edge length of 250 m, an upper western edge length of 1000m, an included angle of 120°, a lower southern edge length of 120 m, a lower western edge length of 1200m, an average height of 150 m, resulting in a total encumbered coal volume of 13.7 million tons. This approach effectively recovered 39.3 million tons of resources previously encumbered in the northeastern deformation zone. These achievements provided substantial technical support for the safe production of the Baiyinhua No. 1 Open-pit Coal Mine and offered valuable experience for slope stability-controlled mining in open-pit mines with composite coal seams and soft rock conditions.