The invention provides a special portable miniature drainage cover for automatic underwater local dry-method welding. A drainage cover body of the drainage cover comprises an upper end cover, an organic glass cover and a lower end cover. A clamping rod, an air inlet quick plug connector, a lower locking sleeve, a cooling air chamber and an underwater camera component are fixed to the upper side of the upper end cover and the lower side of the upper end cover through threaded connection respectively, and the upper end cover and lower end cover are connected with the organic glass cover through threads. A welding oscillator is clamped on the upper portion of a copper welding torch of a welding gun. According to the structure of a drainage sealing device, drainage felt and a felt skirt are arranged on the periphery of the lower end cover, and the drainage felt and the felt skirt are fastened on the lower end cover through hose clamps; the copper welding torch of the welding gun is fastened through an upper locking sleeve and the lower locking sleeve, the welding gun is inserted into the organic glass cover, and an elastic rubber leather sheath is arranged between the upper locking sleeve and the lower locking sleeve. The special portable miniature drainage cover for automatic underwater local dry-method welding has the advantages of being simple in structure, exquisite, convenient and fast to use, low in cost, obvious in drainage effect, and stable and reliable in welding process. Moreover, a connector with the quality of on-land welding is formed, the welding efficiency is improved and the special portable miniature drainage cover is easy to popularize.