The new development of high power femtosecond fiber laser system is reviewed, including single femtosecond fiber chirped pulse amplification, spatially divided coherent beam combination, divided-pulse amplification coherent combination, nonlinear compression and spectral coherent beam combination, etc. The characteristics of these techniques are analyzed and it is pointed out that the coherent polarization beam combining technology based on active phase control is the most promising approach for developing high power femtosecond fiber laser system.