The invention belongs to the field of optical device machining, and discloses a grinding and polishing device and method for an optical cone. The device comprises a supporting frame, a movable mechanism, an ejector pin, a plane polishing disc and a polishing disc motor, wherein the movable mechanism is installed on the supporting frame and has two movable degrees of freedom, namely the first degree of freedom of end part rotation and the second degree of freedom of which the rotation center is perpendicular to a rotating shaft at the end part; the end part of the movable mechanism is used forbeing connected with the to-be-machined cone; the ejector pin is located in a plane where the rotating shaft at the end part of the movable mechanism moves in the second degree of freedom; and the plane polishing disc is universally connected with the ejector pin, the ejector pin is connected with the polishing disc motor through a shaft, and a polishing material layer is arranged on the surface of the plane polishing disc. The cone is connected to the shaft end of the movable mechanism, the contour line of the cone is adjusted to be horizontal, the cone is polished along a track forming a spiral line around the axis of the cone, and the rotating speed of the cone is controlled according to the pressure born by the plane polishing disc and the moving speed, rotating speed, swinging speed and amplitude of the plane polishing disc.