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We report a passively mode-locked thulium, holmium-codoped fiber laser with graphene saturable absorber. Stable nanosecond pulse with output pulse energy up to 35 nJ is obtained at the repetition rate of 0.964 MHz. The tunable output spectral range is from 1897.69 to 1930.27 nm by simply changing the pump power. Higher output pulse energy is promising but limited by the damage threshold of the fiber component.