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In this study, we applied historical matching and self-analogism methods, as well as laboratory physical-mechanics tests, to study the evolution mechanism of the collapse-slide-flow slide at the waste dump on the slope of the chair-shaped gully, as well as the evolution mechanism of the subsequent debris flow. Our analyses indicate that (1) an excessive fine particle content results in a relatively large specific surface area and further enhances water retention performance, (2) rainfall infiltration was concentrated at the contact surface between chair-shaped valley and bottom of the bulk, and (3) with high-intensity continuous rock discharge during the snow and ice period, a mixed frozen body of ice waste stone particles forms, such that ice melting in the spring leads to a sudden change in the shear strength near the contact interface between the waste rock pile foundation and the bulk. Dual effects, essential internal factors, i.e., shear strength and water retention, induced external factors, i.e., ice-freezing skeleton-melting structure collapse, and the chimney effect drive the slope toe of the waste dump. The weak interface of the Quaternary base gradually penetrates the interior of the dumping body, beginning to form from a single-stage traction landslide and evolving into a multi-stage rotary landslide. The sliding surface is characterized by the shear outlet at the front edge of the slope toe, quaternary base interface, and nearly vertical and steep trailing edge. During this movement, gasification on the sliding surface and particle rotation lead to long run-out sliding, which magnifies the scope of disaster.