Carbon nanotubes（CNTs）used as passively mode-locked medium have attracted much attention in ultrafast fiber laser.Advantages include ultrafast recovery time of absorption,high nonlinearity,simplicity of fabrication,low cost,broadband operation,compatibility with fiber,device flexibility.CNT-based saturable absorbers have been successfully realized in different laser structures,such as solid state,waveguide and fiber-type.The paper gives an introduction of the research progress concerning passively mode-locked ultrafast fiber laser,especially those utilize CNTs as the saturable absorbers.