As aeroengines operate in gradually harsher service environments, enhancement of the service temperature and stress tolerance of SiC_f/SiC is in great demand to ensure its proper work in high-temperature air/water-oxygen environments. Previously, researchers have initiated efforts to modify the matrix through self-healing techniques to enhance the oxidation resistance and creep resistance of SiC_f/SiC composites, but whether it can be modified for more severe conditions remained unknown. Here, SiYBC modified SiC_f/SiC composites (MI SiC_f/SiC-SiYBC) were prepared by melt infiltration (MI), and their tensile creep properties and damage mechanisms in air at temperatures of 1300, 1350, and 1400 ℃ with applied stresses ranging from 60 to 120 MPa were explored. The composites were reinforced with plain woven fabric of silicon carbide fibers, while the matrix was prepared by melt infiltration process. The results demonstrate that the creep rupture time ($t_{\mathrm{u}}$) is significantly influenced by stress and temperature, exhibiting a decrease with increasing temperature or stress. When test creep stress exceeds the proportional ultimate stress ($\sigma_{\mathrm{PLS}}$), the matrix cracking facilitates oxygen ingress into the material, leading to erosion of the fiber and BN interfaces and subsequent oxidative degradation, which markedly reduces $t_{\mathrm{u}}$. As a result, the matrix is fully fractured, and the load is mainly supported by the fibers, whose creep resistance becomes the principal factor influencing performance. Conversely, when the creep stress is below $\sigma_{\mathrm{PLS}}$, $t_{\mathrm{u}}$ is extended, with the load being borne by the fibers and the matrix, which is controlled by the combined creep resistance of fibers and matrix. Additionally, as the temperature increases from 1300 to 1400 ℃, the generated oxides fill the gap of the matrix/fiber interface, enhancing interfacial bonding and facilitating crack propagation and growth.