In this study, a novel hybrid plasma waveguide with a cylindrical air gap and fully symmetrical metal and gain medium triangular ribs was designed. The two- and three-dimensional coupled electric-field-distribution models of the waveguide were built using COMSOL Multiphysics software. The mode characteristics of the waveguide were analyzed based on the finite element method. Results indicate that the designed waveguide exhibits strong optical field constraint capability, overlong propagation distance, ultra-low propagation loss, and gain threshold at 1550-nm operating wavelength. We optimize the structural parameters of the waveguide, and when the effective mode field area of the waveguide reaches 0.0022λ2, the propagation length and propagation loss are 69805 nm and 0.0017, respectively. Furthermore, the laser based on the waveguide exhibits a low gain threshold of 49.3 cm -1. Finally, the tolerance of the waveguide performance against these possible fabrication imperfections is analyzed. It is concluded that the waveguide structure exhibits good tolerance to possible fabrication imperfections. Compared with the same type of waveguide structures with air gap, the waveguide demonstrats good comprehensive performance and great potential in various integrated nanophotonic devices.