The invention discloses a device and a method for automatic helical milling of a hole. The device comprises a base, a spindle slide base, an outer eccentric sleeve, an inner eccentric sleeve, a torque motor, a circular grating, an electric spindle, a presser foot, an industrial camera, a linear grating, four laser distance sensors, a servo motor, a ball screw assembly, a synchronous belt and the like, wherein axes of inner and outer contours of the inner and outer eccentric sleeves have offsets; the inner eccentric sleeve is installed in the outer eccentric sleeve; and the axis of the inner contour of the outer eccentric sleeve and the axis of the outer contour of the inner eccentric sleeve are coincident. The device and the method have the advantages that the tool radial offset is realized through control of a relative rotation angle between the inner eccentric sleeve and the outer eccentric sleeve; in spindle feeding, a double-grating feedback technology is adopted so that dimple depth accuracy is guaranteed; and a preset hole position on a workpiece is detected by the industrial camera and a normal vector of the preset hole position is detected by the four laser distance sensors and the industrial camera and the four laser distance sensors cooperate with automatic numerically-controlled devices such as an industrial robot, a numerically-controlled machine tool and the like and thus high-precision and high-efficiency automatic hole milling is realized.