We report an all-normal-dispersion ytterbium fiber laser mode locked by nonlinear polarization evolution.With a 347-m-long all-fiber ring cavity,a pulse energy of 263 nJ at a repetition rate of 613 kHz is achieved,which is the highest per-pulse energy directly obtained from an all-fiber mode-locked laser doped by ytterbium ions.The compact and operation-robust laser yields a well-shaped spectrum centered at 1032 nm with a bandwidth(FWHM) of 4 nm,and the slope efficiency is as high as 27.5%.The proposed low-repetition-rate high-pulse-energy mode-locked fiber laser will be a promising seed for all-fiber chirped pulsed amplification systems. We report an all-normal-dispersion ytterbium fiber laser mode locked by nonlinear polarization evolution. With a 347-m-long all-fiber ring cavity, a pulse energy of 263 nJ at a repetition rate of 613 kHz is achieved, which is the highest per-pulse energy directly obtained from an all-fiber mode-locked laser doped by ytterbium ions. compact and operation-robust laser yields a well-shaped spectrum centered at 1032 nm with a bandwidth (FWHM) of 4 nm, and the slope efficiency is as high as 27.5%. The proposed low-repetition-rate high-pulse-energy mode-locked fiber laser will be a promising seed for all-fiber chirped pulsed amplification systems.