A long-cavity mode-locked Yb-doped fiber laser is reported. The laser consists of only single mode fiber (SMF) components except the nonlinear polarization rotation (NPR) parts which are utilized to achieve self-starting mode-locking, and operates at the all-normal-dispersion (ANDi) region since there are no dispersion compensation elements inside the cavity. Dissipative solitons were obtained via the introduction of only a narrow-bandwidth spectral filter into the pulse shaping process. Two long-cavity conditions were implemented by lengthening the SMF, where pulses with 6.66 MHz repetition rate and 12 nJ single pulse energy and those with 5.05 MHz repetition rate and 20 nJ single pulse energy were obtained respectively, both showing a noise suppression ratio of 75 dB on the radio frequency (RF) spectra. Compared to the former ANDi mode-locked fiber lasers, this laser operates at a lower repetition rate with higher single pulse energies and better stability, which should be useful in the construction of a simplified fiber chirped pulse amplification (CPA) system.