Homoepitaxial　growth　of　step-flow　single　crystal　diamond　was　performed　by　microwave　plasma　chemical　vapor　deposition　system　on　high-pressure　high-temperature　diamond　substrate.　A　coarse　surface　morphology　with　isolated　particles　was　firstly　deposited　on　diamond　substrate　as　an　interlayer　under　hillock　growth　model.　Then,　the　growth　model　was　changed　to　step-flow　growth　model　for　growing　step-flow　single　crystal　diamond　layer　on　this　hillock　interlayer.　Furthermore,　the　surface　morphology　evolution,　cross-section　and　surface　microstructure,　and　crystal　quality　of　grown　diamond　were　evaluated　by　scanning　electron　microscopy,　high-resolution　transmission　electron　microcopy,　and　Raman　and　photoluminescence　spectroscopy.　It　was　found　that　the　surface　morphology　varied　with　deposition　time　under　step-flow　growth　parameters.　The　cross-section　topography　exhibited　obvious　inhomogeneity　in　crystal　structure.　Additionally,　the　diamond　growth　mechanism　from　the　microscopic　point　of　view　was　revealed　to　illustrate　the　morphological　and　structural　evolution.