In this article, we report an efficient sub-nanosecond pulses generation in Yb-doped fiber laser with 400 kHz repetition rate and 960 ps pulse width, which adopts master oscillator fiber power amplifier (MOPA) configuration, extracting 8.9 W average output power up to 23 kW with central wavelength of 1064.5 nm. The seed laser with 100 mW average output power is amplified to 8.9 W by one-stage Yb-doped double-cladding fiber amplifier, pumped by 6 multimode laser diodes with maximum output power of 10 W. This kind of high-energy sub-nanosecond Yb-doped fiber laser can be widely used in material processing, laser radar, laser ranging and other fields.