In　situ　scanning　electron　microscopy　(SEM)　offers　a　good　way　to　investigate　the　structural　evolution　during　lithiation　and　delithiation　processes.　In　this　paper,　the　dynamical　morphological　evolution　of　3D-line-structured/unstructured　Si/C　composite　electrodes　was　observed　by　in　situ　SEM.　The　investigation　revealed　the　microstructural　origin　of　large　charge　capacity　for　3D-line-structured　anodes.　Based　on　this　proposed　mechanism,　a　coarse　optimization　of　3D-line-structured　anodes　was　proposed.　These　results　shed　light　on　the　unique　advantages　of　using　an　in　situ　SEM　technique　when　studying　realistic　bulk　batteries　and　designing　3D　electrode　structures.