Dislocation　emissions　on　the　slip　plane　from　crack　tips　in　silicon　were　observed　through　transmission　electron　microscopy.　The　effects　of　the　slip　plane　orientation　and　load　on　dislocation　emission　or　plastic　zone　have　been　investigated.　The　results　show　that　the　angle　between　slip　plane　and　crack　plane　has　an　effect　on　dislocation　structure　and　plastic　zone　under　the　I　mode　load,　and　the　direction　of　the　movement　of　dislocation　emission　may　change　along　the　direction　of　the　maximum　shear　stress,　or　move　in　zigzag　on　different　slip　planes　alternatively.　The　experimental　average　22.0　nm　of　dislocation　width　approximates　to　23.6　nm　calculated　by　Peierls　dislocation　model.