The utility model relates to a fixture, in particular to a fixture for machining a tee joint. The fixture for machining the tee joint comprises a machine base, an index workbench, a positioning device and a pressing device. The machine base is of a bent plate structure with a conical shaft, the conical shaft is matched and connected with a lathe spindle hole, the index workbench is a vertical type part with two vertical V-shaped grooves, a threaded hole is formed in the upper end of the index workbench, a positioning hole B and a small conical shaft are arranged at the lower end of the index workbench, and the small conical shaft is matched and connected with a circular conical hole in the machine base. The pressing device is composed of a sizing block, a nut A, a screw rod and a pressing plate, the screw rod is connected with the threaded hole in the index workbench, the positioning device is composed of a nut C, a positioning pin, a blocking table and a spring, and the positioning pin is matched and connected with the positioning hole A in the machine base. The fixture for machining the tee joint has the advantages that when the other end of the machined tee joint is changed on a lathe, cutting feeding and turning can be conducted directly without correcting, the efficiency is improved, and time and labor are saved.