Geopolymer repair materials, known for their superior corrosion resistance, high strength, and environmentally friendly properties, are increasingly used to repair concrete structures. However, during the curing process, especially in thick-layer repairs, geopolymers often develop initial defects due to hydration reactions, alkali-silica reactions, and shrinkage, with microcrack formation being prevalent. These defects can significantly impair the material’s erosion resistance. To investigate the influence of these defects on erosion resistance, this study employed molecular dynamics (MD) simulations to examine the effects of various defects, corrosive solutions, and coating protection. The findings show that initial defects create pathways for the penetration of water molecules and ions, leading to an up to 17.5 % increase in ingress. Additionally, chloride (Cl^-) and sulfate ions (SO₄^2-) interact with the geopolymer substrate, further speeding up destruction. In contrast, the application of a silane coating reduces ion and water penetration by nearly 11.5 %, forming a protective hydrogen-bonded layer that markedly enhances erosion resistance. This study provides valuable insights for optimizing erosion resistance in geopolymer repair materials and supports the effectiveness of coating techniques in practical applications.