Abstract: The catalytic recombination, oxidation, and nitridation coupling processes occurring at the gas-solid interface between the high-enthalpy flow and thermal protection materials are key factors influencing the aerodynamic thermal environment. Real-time measurement of the near-wall gas temperature and atomic number density under high-enthalpy conditions is essential for understanding these coupling mechanisms. In this study, laser absorption spectroscopy was employed using the oxygen atomic line at 777.19 nm and the nitrogen atomic line at 868.03 nm to quantitatively determine the translational temperature and species number density at different spatial positions near the surface of a C/SiC composite material. Two optical paths were selected: at position 1, the laser beam center was close to the material surface; at position 2, it was approximately 2 mm away. Simultaneously, the emission spectra of ablation products (CN and Si) were collected at position 1. The high-enthalpy aerodynamic thermal environment was generated using a 1 MW high-frequency inductively coupled plasma wind tunnel. Considering the surface temperature and post-ablation morphology of the C/SiC material, two experimental conditions with distinct surface oxidation characteristics were designed. Condition 1 featured a total enthalpy of 43.2 MJ/kg and a heat flux of 3.7 MW/m², while condition 2 had 37.5 MJ/kg and 3.1 MW/m², respectively. The heating duration for both conditions was 120 s. The laser absorption spectroscopy results indicate that, due to shock wave compression effects, position 1 near the wall exhibits lower translational temperature but higher number density compared to position 2 farther from the wall. Both conditions show significant decreases in translational temperature and O/N atom number density at position 1. Concurrently, the prominent CN radiation observed at Position 1 indicates substantial nitridation reactions. Scanning electron microscopy and energy dispersive spectroscopy analyses confirm that the material surface is covered with an SiO₂ layer. Relative to condition 2, condition 1, characterized by higher enthalpy and heat flux, exhibited a more pronounced reduction in the near-wall number densities of both O and N atoms. This observation, in conjunction with stronger radiative intensity of CN and Si, as well as a reduced surface oxygen concentration, collectively implies that the surface oxide layer is more prone to volatilization or consumption, and the competitive process between oxidation and nitridation reactions is more intense under State 1. This research demonstrates that spatiotemporally resolved measurements of key parameters, such as the number densities of near-wall species and their radiative spectra, provide critical insights into the complex coupling processes at the gas-solid interface.