A bendable transmission line (TL) of spoof surface plasmon polaritons (SSPPs) is presented, which can maintain good transmission performance despite of the deformation caused by bending. Such a TL consists of flexible dielectric substrate and ultrathin metallic strip with zigzag decorations that are designed to support the propagation of SSPPs with strong field confinement and low radiation loss. Furthermore, the proposed SSPP TL is used to excite an amplifier chip efficiently, reaching high and stable gains with nearly no degradation of amplification in the bending states. Numerical and experimental results are demonstrated to verify the bendable merits of both passive TL and active amplifier from 12 GHz to 18 GHz. The flexible and stable characteristics of this design may find utility in novel applications like wearable electronics and conformal plasmonic circuits in the microwave frequencies.