The invention discloses a slow wave structure of a coplanar waveguide, wherein the slow wave structure of the coplanar waveguide belongs to the technical field of microwave electrovacuum and relates to a travelling wave tube amplifier device. The slow wave structure of the coplanar waveguide comprises a dielectric substrate (2) and a metal layer (1) on the surface of the dielectric substrate (2). The metal layer (1) comprises a central conduction band and grounded metal surfaces at two sides of the central conduction band. The shape of the central conduction band is a periodical bent curve. The central conduction band is isolated from the grounded metal surfaces at two sides. The slow wave structure of the coplanar waveguide can effectively settle a problem of electron accumulation on a microstrip slow wave structure, and serial connection or parallel connection with other microwave devices is easily realized, thereby easily realizing small size and integration of a vacuum device. The vacuum device with the structure of the invention has relatively low working voltage, and the coupling impedance curve and the dispersion curve are relatively flat, thereby realizing wide frequency band of the vacuum device and reducing gain fluctuation of the vacuum device in the working frequency band. Therefore the slow wave structure of the coplanar waveguide has relatively high potential and is suitable for a miniature planar travelling wave tube.