The Transition Radiation Detector of AMS 02

The Alpha Magnetic Spectrometer AMS02 is equipped with a large transition radiation detector (TRD) ready for particle identification. The positron/proton separation is essential for searching for the indirect Dark Matter signals in cosmic rays. Discrimination at 10$^{2}$ to 10$^{3}$ level between positron and proton with energy up to 300 GeV has been achieved. Readiness and maintenance free operation for more than three years in space, testing and current cosmic ray measurements will be discussed.