Passive　Q-switching　and　passive　mode-locking　are　the　key　technologies　for　ultrafast　laser　to　achieve　ultrashort　pulse　and　ultrahigh　peak　power.　The　transition　metal　dihalides　(TMDs)　turn　to　be　promising　saturable　absorber　(SA)　materials　due　to　its　outstanding　characteristics　of　wide-band　absorption　effect,　third-order　nonlinear　magnetic　susceptibility　and　high　carrier　mobility.　The　optical　and　physical　properties　of　different　TMDs　are　affected　by　the　composition　and　structure.　In　this　review,　a　variety　of　SA　with　different　transition　metals　and　chalcogens　have　been　discussed.　Also,　the　breakthrough　research　on　defect　regulation　based　on　TMDs,　combination　of　heterostructures　were　emphasized.　Furthermore,　the　future　prospects　and　challenge　have　also　been　addressed.