The invention discloses a portable circular ring end surface milling machine, and relates to o a milling machine, which comprises a lateral arm (4), a feeding device, a milling device and a positioning clamping device, wherein the upper portion of the positioning clamping device is provided with the feeding device, the upper portion of the feeding device is provided with the lateral arm, one end side surface of the lateral arm is provided with the milling device, the positioning clamping device comprises a positioning disk (13), supporting foot seats (14) and adjustment screw rods (15), the positioning disk presents the octagonal prism shape and comprises eight side surfaces, the eight side surfaces of the positioning disk are provided with the four sets of the support foot seats at intervals, the outer end surfaces of each set of the support foot seat are respectively provided with screw rod seats (11) arranged in a regular triangle arrangement manner, and one end of the adjustment screw lock is fixed in the screw rod seat through a locking nut (23). According to the present invention, the positioning clamping device is adopted to perform positioning and fixing, and the rotary support of the rotary active joint and the frame-type cantilever are adopted, such that the excessive bending moment produced during the milling process is overcome, and the purposes of stable milling and milling system rigidity improving are achieved.