Mid-infrared laser has important application value in many fields, such as communication, remote sensing, security inspection, optoelectronic countermeasures, and so on, and has always attracted enormous attention. There are many methods for generation of mid-infrared laser, among which mid-infrared fiber lasers have the characteristics of compact structure, good beam quality, and high conversion efficiency, and so on, so they are considered as the most promising way to achieve portable, stable, efficient, and high-power mid-infrared laser emission. With the improvement of manufacturing technology of soft glass fibers, mid-infrared fiber laser technologies have achieved rapid development, and the output power level has also been greatly enhanced. However, limited by the types of rare earth ions, the fabrication process and chemical stability of soft glass fibers, the mid-infrared lasers based on soft glass fibers have technical difficulties in further improving the power and expanding the wavelength. The mid-infrared fiber gas lasers appeared in recent years provide an effective solution to these problems. The research status of mid-infrared fiber laser technologies are reviewed in detail, including the new mid-infrared fiber lasers based on gas-filled hollow-core fibers, and the development trend of mid-infrared fiber laser technologies is briefly prospected.