To improve the AO erosion resistance of siloxane coating, the Si ion implantation with nominal dosage of 7×1016 ions/cm2 in siloxane coatings on the polyimide substrate was carried out by using the plasma immersion ion implanter. The Si implanted siloxane coatings before and after AO exposure in the ground-based AO simulation facility were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS). The results of mass measurement shown that, in initial stage of AO exposure the implanted sample had a small mass change, and then was stabilized. The erosion yield of the implanted siloxane coating decreased by a factor of more than two orders of magnitude compared with that of the polyimide film, and decreased by a factor of more than an order of magnitude than that of unimplanted siloxane coatings. The results through SEM and XPS indicated that a continuous high-quality protective SiO2 surface layer was formed on the implanted siloxane coatings after the AO exposure. It can prevent further degradation of the underlying polymer with increased exposure to the AO flux and provide high-quality erosion protection for these materials. The Si implanted materials have a markedly increased erosion resistance than unimplanted siloxane coatings in AO environment.