Abstract: A multi-beam continuous transverse stub (CTS) array antenna for millimeter wave based on substrate-integrated waveguide (SIW) is proposed in this paper. The antenna consisits of three parts: feed horns, the plane wave conversion structure and radiating part. The feed horns are based on SIW, with a matching structure added to the aperture to improve radiation performance. The plane wave conversion structure is composed of a SIW parabolic reflective surface and gradual coupling slots, which can convert the column cylindrical surface wave radiated from the feed horns into plane wave with amplitude obeying Taylor distribution. Therefore, the antenna has the characteristic of low side lobe. The radiating part is a 1×8 CTS array with optimal stub widths to ensure that the array elements radiate equivalent power. The antenna works at 30 GHz, and the beam switching within ±20° can be achieved by changing the input ports. The antenna measure results are consistent with the simulation results, verifying the rationality of the design. The antenna has the advantages of high gain, low profile and stable performance, which can be processed using the PCB technology.