High-power ultrafast lasers have a wide range of applications, such as precise industrial processing, ultrafast spectroscopy, high-field physics, and military applications. Fiber lasers have the advantages of convenient operation, thermal load insensitivity, and good beam quality. The recent research progress of high-power ultrafast fiber lasers is reviewed, including the emerging passive mode locking and chirped pulse amplification technologies. The advantages of high-power fiber lasers on nonlinear optics are discussed via an example application, namely using high-power ultrafast fiber lasers to generate high-order harmonics. Further, the potential future research directions have also been prospected.