Widely employed in fundamental research, industrial processing, and biomedicine, femtosecond fiber lasers exhibit many attractive features such as high average power, good heat dissipation, excellent beam quality, and compact footprint. Coherent combining technology can effectively suppress the detrimental nonlinear and thermal effects in the fiber amplifiers, and therefore further increase the output pulse energy and average power of femtosecond fiber lasers. In this article, we mainly discuss different coherent combining techniques in high-power ultrafast Yb-fiber laser systems and the relevant phase-locking methods. We believe that the advent of new coherent combining techniques will further improve the average power and pulse energy of femtosecond fiber laser systems, thereby opening up some new research areas.