Due to awareness of climate change and rising of oil price, researches for eco-friendly vehicles or the related fuel saving technology are actively progressed. In this research, CGST(Clutchless Geared Smart Transmission) as new smart transmission which is eco-friendly and comfortable is proposed. And we designed structure of the test bench for verifying the performance of CGST. CGST can improve the comfort and durability of transmission by using a planetary gear set and a motor generator instead of conventional clutch. And as new smart transmission, the motor generator in CGST makes mild hybrid function possible, so the high fuel efficiency is obtained. CGST is rated as the system supplementing the weakness of DCT(Dual Clutch Transmission) and AMT(Automated Manual Transmission). In this paper, we performed structural design of the planetary gear and the multi-axes transmission and selected the motor/generator. Furthermore, we proposed the CGST control logic. The structural design of CGST test bench will play on important role in development of CGST for verifying the operational and torque transferring performance. And CGST test bench will be also used for developing the CGST control logic.