An expansion tube facility was operated using two half-cylinder models with width of 45 mm and 90 mm respectively for producing high-enthalpy flows at the nominal velocity of 8 km/s relevant to Earth reentry. Spatially resolved emission spectroscopy in the wavelength range from 250 nm to 550 nm behind a shock wave was recorded by a spectrometer with ICCD camera. Shock wave stagnation streamline was observed along the flow direction. It is found that the spectrum are dominated by the CN(B-X) violet band. A halogen tungsten lamp was used to realize calibration and the absolute radiation luminance of the shock layer was obtained. By comparing the model widths normalized by two kinds of model radiances, it can be found that there is a strong self-absorption of high temperature gas radiation around the flow fluid. In addition, three-dimensional effect was observed. It can be found that the ratio between spectral radiance at 385.2 nm in the CN(B-X) violet 3-3 band and spectral radiance at 388.4 nm in the CN(B-X) violet 0-0 band is decreasing along the distance toward the model edge. The results illuminated that dynamical non-equilibrium features exists in the shock layer along the distance of the model edge.