The　growth　mechanism　about　CVD　diamond　films　on　(001)　surface　was　studied　with　first-principle　method　which　was　based　on　density　functional　theory　(DFT).　The　configurations　of　clean　diamond　surface　and　H-terminated　diamond　surface　were　calculated.　The　adsorption　evolutions　of　H　atoms　and　radicals　(C,　CH,　CH2　and　CH3)　on　the　surface　of　diamond　reconstruction　and　the　surface　of　monolayer　H-terminated　diamond　were　analyzed.　The　results　indicate　that　a　clean　diamond　surface　undergoes　a　symmetrical　dimer　reconstruction　transformation　and　a　monolayer　H　adsorbed　on　the　surface　can　lead　to　stable　of　the　diamond　structure.　In　addition,　H　atoms　can　activate　graphite　and　extract　H　to　make　a　radical　site　when　radicals　are　adsorbed　on　the　diamond　(001)　surface.　CH2　groups　can　better　improve　the　growth　rate　of　CVD　diamond　film　than　CH3　groups.　CH2　group　is　the　most　efficient　group　in　the　process　of　CVD　diamond　film　growth.　CH　group　hinders　the　growth　of　CVD　diamond　film.