A cascaded ytterbium-doped all-fiber master oscillator power amplifier (MOPA) with 1064-nm pulsed laser is demonstrated, and it can produce up to 20-W average power and 0.1-mJ pulse energy at tunable repetition rates from 10 to 200 kHz. Two main di±culties of the all-fiber configuration are overcome: all fiber isolator and mode field adapter between single mode fiber (SMF) and double cladding fiber (DCF). Gain saturation and nonlinear effect are analyzed theoretically, and the possibility of further power-scaling of this cascade scheme is predicted.