In order to improve the compactness and properties of C/C-SiC-ZrC composites produced by precursor infiltration and pyrolysis (PIP) method, the low-temperature reactive melt infiltration process (RMI) was used to seal the composites using Zr2Cu as the filler. The microstructure, mechanical properties and ablation properties of the Zr2Cu packed composites were analyzed. During Zr2Cu impregnation, the melt efficiently filled the large pores of the composites and converted to ZrCu due to a partial reaction of zirconium with carbon. This resulted in an increased composite density of 2.24 g/cm3 and a 27.35% reduction in open porosity. Additionally, the flexural strength of Zr2Cu packed C/C-SiC-ZrC composites improved from 122.78±8.09 MPa to 135.53±5.40 MPa. After plasma ablation for 20 s, the modified composites demonstrated superior ablative resistance compared to PIP C/C-SiC-ZrC, with mass ablation and linear ablation rates of 2.77×10-3 g/s and 2.60×10-3 mm/s, respectively. The “self-transpiration” effect of the low melting point copper-containing phase absorbed the heat of the plasma flame, further reducing the ablation temperature and promoting the formation of refined ZrO2 particles within the SiO2 melting layer. This provided more stable erosion protection for Zr2Cu packed C/C-SiC-ZrC composites.