We report all-normal-dispersion passively mode-locked Yb-doped fiber laser by graphene epitaxially grown on 6H-SiC substrates in a ring cavity configuration. Stable mode-locked pulses of the fiber laser are obtained at about 250 mW incident pump power and the pulse repetition rate is 1.05 MHz; Increasing the incident pump power to 480 mW, the average output power is 20 mW, which corresponds to single pulse energy of up to 19 nJ with pulse width of about 520 ps.