High harmonic generation (HHG) with tunable spectral characteristics by intense laser-plasma interaction has long been a research hotspot both in China and abroad. In this study, a two-dimensional particle simulation program is employed to investigate the radiation characteristics of the HHG by the plasma waveguide driven by an ultra-short ultra-intense laser pulse and the related dynamic behavior of the electrons. The influences and regulation laws of key parameters, including driving laser intensity and plasma density, on the conversion efficiency and ellipticity of the HHG are discussed, and their underlying physical mechanisms are analyzed by the Baeve-Gordienko-Pukhov (BGP) theory. This study provides a novel technical route for developing high-brightness, ultra-short ultra-fast, and circularly polarized mesa-type radiation sources in the wavelength range from deep ultraviolet to soft X-ray and is thus expected to further facilitate the development of ultrafast ultra-high-sensitivity techniques for chirality detection.