The invention discloses a collapse type sleeve floating coupling which comprises a shell, an outer ring partition plate, an inner ring partition plate, a slide plug and a shear pin. The shell is of a tubular structure. A conical shoulder is arranged in the middle of the inner wall of the shell. The outer ring partition plate is formed by tightly arranging a plurality of fan-shaped partition plate bodies and a plurality of trapezoid-like partition plate bodies sequentially at intervals and located at the conical shoulder. The inner ring partition plate is formed by tightly arranging a plurality of fan-shaped partition plate bodies and a plurality of trapezoid-like partition plate bodies sequentially at intervals and located at the inner conical face of the inner side of the outer ring partition plate. The slide plug is of a cylindrical structure and is located in the center of the inner ring partition plate and connected with the inner ring partition plate through the shear pin. According to the scheme, the risk of blocking and clamping in a sleeve can be eliminated through the collapse inner structure, and major well cementing quality accidents are avoided; and the communication breaking pressure can be adjusted by changing the material and the diameter of the shear pin, smooth well cementing construction is guaranteed, and it is ensured that application requirements for a sleeve floating technology are fully met. The invention further discloses a well cementing assembly and method adopting the collapse type sleeve floating coupling.