Mid-infrared ultrafast fiber lasers are widely used in many aspects such as laser medical treatment, military, atmospheric monitoring, and biology. It has become a key research direction in the field of laser technology in recent years. Thanks to the rapid development of mid-infrared laser gain materials and mode-locked technology, the research and the development of mid-infrared ultrafast fiber lasers are promoted [81-84]. Until now, the ultrafast fiber laser CPA system of the highest average output power at 2μm has reached multi kilowatts, and the output wavelength has been extended to 3.5μm. In this paper we have summarized the research progress of mid-infrared ultrafast optical fiber lasers and amplifiers in recent years. In addition, the main mode-locking technology in different optical bands, as well as the femtosecond fiber laser technology to achieve narrower pulse width and longer wavelength are introduced. But there still exist many challenges for mid-infrared ultrafast fiber lasers. First, high-efficiency gain ions have always been lacking in the infrared wavelengths, especially in the long-wavelength band. Secondly, the mid-infrared mode-locked devices and mode-locked technology have made significant progress in recent years, which are the key factors to improve the mode-locked lasers. However, compared with the mature saturable absorbers in the near-infrared region, the recovery time, unsaturated loss, damage threshold and other parameters of the existing infrared saturable absorber still has a lot space to be optimized. There still needs a lot of work to develop new saturable absorption materials and ultra-short mid-infrared pulse mode-locked technology, and the precise formulation of specific parameters of saturable absorbers is still an important topic for future research. It can be believed that high average power, high pulse energy and long-wavelength-infrared ultrafast fiber lasers will become a competitive technology with its practicability in the near future.