Abstract: Hydrogen and then helium were implanted into Si samples. Then these samples were annealed at different temperatures. It was found that the total dose of co-implantation which cause blistering and exfoliation on the surface was much smaller than the dose of hydrogen and helium implanted separately. In this work, RBS/C （Rutherford Backscattering Spectroscopy and Channeling）, X-ray Four-Crystal Diffractormeter, AFM （Atom Force Microscopy） and XTEM （Cross Sectional Transmission Electron Microscopy） were used to characterize these samples. Some results were then computer simulated and the mechanism was discussed.