The　single-layer　molybdenum　disulfide　(SLMoS2)　nanosheets　have　been　experimentally　discovered　to　exist　in　two　different　polymorphs,　which　exhibit　different　electrical　properties,　metallic　or　semiconducting.　Herein,　molecular　dynamics　(MD)　simulations　of　nanoindentation　and　uniaxial　compression　were　conducted　to　investigate　the　phase　transition　of　SLMoS2　nanosheets.　Typical　load-deflection　curves,　stress-strain　curves,　and　local　atomic　structures　were　obtained.　The　loading　force　decreases　sharply　and　then　increases　again　at　a　critical　deflection　under　the　nanoindentation,　which　is　inferred　to　the　phase　transition.　In　addition　to　the　layer　thickness,　some　related　bond　lengths　and　bond　angles　were　also　found　to　suddenly　change　as　the　phase　transition　occurs.　A　bell-like　hollow,　so-called　residual　deformation,　was　found　to　form,　mainly　due　to　the　lattice　distortion　around　the　waist　of　the　bell.　The　effect　of　indenter　size　on　the　residual　hollow　was　also　analyzed.　Under　the　uniaxial　compression　along　the　armchair　direction,　a　different　phase　transition,　a　uniformly　quadrilateral　structure,　was　observed　when　the　strain　is　greater　than　27.7%.　The　quadrilateral　structure　was　found　to　be　stable　and　exhibit　metallic　conductivity　in　view　of　the　first-principle　calculation.