The invention discloses a welded adjustable reamer. The welded adjustable reamer comprises a reamer bar, a reamer bit and a water cooling hole, wherein the reamer bit is arranged on the front end of the reamer bar; the water cooling hole is coaxially arranged in the middle of the reamer bar; the reamer bit also comprises cutting edges and chip grooves; the cutting edges are arranged around the reamer bit at equal intervals; each chip groove is arranged between every two adjacent cutting edges. Through the structure, the welded adjustable reamer provided by the invention has the advantages that the reliability performance is high, the structure is compact, the radius of the reamer is compensable, the water-cooling temperature reduction is realized, the reamer machining speed is high, the service life is long and adaptability is good, meanwhile, the welded adjustable reamer has broad market prospect in the machining market.