With the development of ultra-high capacity optical communication technology, dense wavelength division multiplexing (DWDM) technology is widely used. For DWDM technology, a stable high repetition rate ultrafast pulse laser source is required. If multiple single-wavelength mode-locked lasers are used as signal sources, the cost and complexity of the system will be very high. While dual-wavelength mode-locked laser, due to its advantages of dual-wavelength output, short pulse duration, good beam quality, and wide tunable wavelength range, can overcome the disadvantage of multiple single-wavelength mode-locked lasers, and effectively meet the requirements for ultra-high capacity optical communication technology. In addition, this kind of light source is also widely used in the fields of spectroscopy and microwave generation. Dual-wavelength mode-locked fiber lasers can be realized using dual-resonator structure, high nonlinearity of two-dimensional materials and intra-cavity filtering effect. Specifically, intracavity filtering effect can be introduced by inserting filter devices directly into the laser resonator, using multimode interference or using nonlinear effects such as nonlinear polarization rotation. At present, the output wavelength of dual-wavelength mode-locked fiber lasers is mainly concentrated in the spectral region of 1μm and 1.5 μm band, and the output power is about milliwatt level. In the future, the laser will develop to achieve the output with mid-infrared or even longer wavelength, as well as the average power of watt-level.