A simple specimen retrieval device for minimally invasive surgery, comprising: an endobag, a variable-diameter assembly for endobag collection and release, an elastic opening expansion mechanism, and an opening closure assembly, wherein the variable-diameter assembly for endobag collection and release is a cylindrical structure formed by curling an elastic sheet-shaped object, and in a natural state, two ends of the elastic sheet-shaped object are partially overlapped and separated from each other; when an outer wall of the cylindrical structure is squeezed by an external force, an area of the overlapped part of the two ends of the elastic sheet-shaped object is configured to gradually increase, and a diameter of the cylindrical structure is configured to gradually decrease; when an inner wall of the cylindrical structure is expanded by the external force, the area of the overlapped part of the two ends of the elastic sheet-shaped object is configured to gradually decrease, and the diameter of the cylindrical structure is configured to gradually increase; the elastic opening expansion mechanism and the opening closure assembly are configured to be disposed in an opening of the endobag; the elastic opening expansion mechanism is configured to automatically expand the opening of the endobag when the external force is not applied; and the opening closure assembly is configured to close the opening of the endobag by overcoming an expansion effect of the elastic opening expansion mechanism on the opening; characterised in that the endobag is configured to be placed in the variable-diameter assembly for endobag collection and release; the variable-diameter assembly for endobag collection and release is suitable to be placed in a trocar cannula. an endobag, a variable-diameter assembly for endobag collection and release, an elastic opening expansion mechanism, and an opening closure assembly, wherein the variable-diameter assembly for endobag collection and release is a cylindrical structure formed by curling an elastic sheet-shaped object, and in a natural state, two ends of the elastic sheet-shaped object are partially overlapped and separated from each other; when an outer wall of the cylindrical structure is squeezed by an external force, an area of the overlapped part of the two ends of the elastic sheet-shaped object is configured to gradually increase, and a diameter of the cylindrical structure is configured to gradually decrease; when an inner wall of the cylindrical structure is expanded by the external force, the area of the overlapped part of the two ends of the elastic sheet-shaped object is configured to gradually decrease, and the diameter of the cylindrical structure is configured to gradually increase; the elastic opening expansion mechanism and the opening closure assembly are configured to be disposed in an opening of the endobag; the elastic opening expansion mechanism is configured to automatically expand the opening of the endobag when the external force is not applied; and the opening closure assembly is configured to close the opening of the endobag by overcoming an expansion effect of the elastic opening expansion mechanism on the opening; characterised in that the endobag is configured to be placed in the variable-diameter assembly for endobag collection and release; the variable-diameter assembly for endobag collection and release is suitable to be placed in a trocar cannula.