Shape　multiformity　and　formation　mechanism　of　shear　band　in　normal　consolidated　soil　were　analyzed　based　on　Modified　Cam-Clay　model　under　plane　strain　condition.　The　results　proved　that　shear　band　forms　because　of　impact　action　caused　by　strain　energy　releasing.　End　restraint　and　initial　defect　can　induce　and　control　the　formation　process　and　shape　of　shear　band.　The　interaction　of　different　boundary　and　initial　defect　settings　was　analyzed　in　order　to　obtain　the　mechanism　and　deformation　process　of　shear　band.