Abstract: CLIC drive beam facility provides required RF power for the CLIC main linac. Drive beam injector produces 4.2A electron bunch trains with 140s pulse length,50Hz repetition rate and about 50MeV energy. In the CLIC drive beam injector the electron gun produces continues beam and the preliminary bunching is done by three sub-harmonic bunchers and one prebuncher. Afterward, the TW buncher continues the bunching and simultaneously, accelerates the beam. This lecture is focused on the preliminary design of this TW buncher.