An all-normal-dispersion ytterbium-doped linear-cavity fiber laser mode-locked by a semiconductor saturable absorber mirror (SESAM) is reported. Without anomalous dispersion part, output pulses are highly-chirped and fundamental repetition rate is 435.6 kHz. Three mode-locking states are observed by adjusting polarization controller and pump power. Characters of these states, such as spectrum, pulse shape and stability, are analyzed in control experiments.