The tube coupling, which is capable of connecting two injectors with different sizes, includes a tube body and a tube connector. The tube body is hollow and has a coupling end and a check valve. The tube connector is coaxially connected to the coupling end of the tube body and has a joint portion. The joint portion has a passage communicating with the tube body. The check valve flexibly closes the passage from the tube body. A diameter of the passage fits a first injector with a first size, and an outer diameter of the joint portion fits a second injector with a second size.
