The　effect　of　etch　damage　to　the　mode　characteristics　of　photonic　crystal　vertical　cavity　surface　emitting　lasers　was　simulated　in　this　paper.　The　devices　simulated　in　this　paper　are　850-nm　GaAs-based　VCSELs　with　photonic　crystal.　And　the　devices　were　simulated　by　using　finite　difference　time　domain　(FDTD)　method.　Limited　to　the　computer　resource,　the　top　DBR　was　simulated　only,　and　the　traverse　size　was　smaller　than　the　real　size.　In　order　to　highlight　the　impact　of　the　etch　damage,　several　kinds　of　light　sources　and　photonic　crystal　structures　were　simulated　separately,　and　each　situation　is　calculated　in　the　condition　of　ideal　photonic　crystal　and　photonic　crystal　with　etch　damage　respectively.　All　parameters　of　device　and　light　feature　are　referred　to　the　real　condition.