The lifetime of Si-based environmental barrier coatings (EBCs) is constrained by thermally grown SiO₂ oxide layer (SiO₂-TGO), which can cause premature cracking and spalling. To address this issue, a new approach for surface modification using aluminum is proposed. The oxidation performance was examined in a 50 vol% H₂O–50 vol% O₂ environment at 1350 °C for up to 300 h. The results indicate that a dense ytterbium aluminum garnet (YbAG) layer was formed after modification, decreasing the porosity by 80%. Due to the elimination of fast diffusion channels and the low oxygen permeability of YbAG, aluminum modification significantly reduced the growth rate of SiO₂-TGO by nearly two orders of magnitude. Consequently, its thickness decreased by more than 70% after 300 h of exposure. A diffusion-controlled oxidation mechanism indicates that the modified dense surface is equivalent to an initial SiO₂ layer with a specific thickness, causing a shift in the oxidation time and increasing the oxidation resistance. This research provides valuable insights for designing Si-based EBC with improved lifetimes.