During high-speed spacecraft reentry into atmosphere, severe aerodynamic heating induces material ablations, which critically affects the structural reliabilities of the key components of spacecrafts. Consequently, replicating the surface local thermal environment during the reentry process of the spacecrafts under ground-based laboratory conditions has emerged as a pivotal research area for national defense and aerospace technology advancement. In this paper, a ground simulation method is established for simulating the local thermal environment of the high-speed reentry vehicles using an argon-oxygen gas mixture discharge plasma arc-jet. On the one hand, a complete and self-consistent physical-mathematical model for non-equilibrium argon-oxygen plasmas is established, including a database for simplified chemical reaction pathways screened with the aid of zero-dimensional hydrodynamic model coupling genetic algorithm and dynamic programming, and transport coefficients under different translational and vibrational non-equilibria, and a set of three-temperature (electron translational temperature, heavy particle translational and vibrational temperatures) governing equations for describing the mass, momentum, energy and charge conservations, as well as the corresponding boundary conditions. Based on the two-dimensional modeling results, a theoretical analysis on the non-equilibrium mass-momentum-energy synergistic transport mechanisms is conducted, and consequently, a method for modulating the local heat flux density to the workpiece is employed mainly by adjusting the chamber pressure except for other operating conditions, e.g., arc current, gas flowrate, stand-off distance between the exit of the plasma generator and the workpiece. On the other hand, an argon-oxygen plasma arc-jet is generated on the multiphase gas discharge plasma experimental platform (MPX). And the ablation experiments are conducted for the phenolic impregnated carbon ablator (PICA) specimens with specified oxygen concentrations in the argon-oxygen mixtures and wall heat flux densities. The experimental results show that, at low heat flux density levels (e.g., 1.07 MW/m2), the relative deviation of the recession depth between the data of this study and the arc-heated wind tunnel data from NASA decreases from 28% for pure argon plasmas to 15% for 90% argon-10% oxygen gas mixture plasmas. And the XPS (X-ray photoelectron spectroscopy) analysis further validates the ablation mechanisms of PICA in an oxygen-containing plasma environment. Additional materials ablation experiments for stainless steel and aluminum alloy ball-head specimens also show significant relative discrepancies in both mass loss and recession depth under the pure argon and argon-oxygen plasma conditions, which further confirms the significant role of oxygen partial pressure on the materials ablation behaviors under low heat flux densities. The ground simulation method based on a plasma arc-jet jet proposed in this study provides a cost-effective preliminary experimental approach for evaluating the materials ablation performances prior to formal and expensive testing in arc-heated wind tunnels.