Abstract: Because ultra short optical pulses can be obtained from a mode-locked fiber laser, it can be applied in many fields.The principle, structure and new evolution of mode-locked fiber lasers were summarized in this paper.The advantage, disadvantages of active,passive and mixed mode-locked technology were analyzed.The new evolution of multi-wavelength mode-lock, stretched pulse mode-lock and photonic crystal based mode-locked techniques were introduced.Finally the latest evolution of mode-locked fiber lasers was discussed and the key issues were pointed out.