We　report　on　a　theoretical　and　experimental　study　of　an　all-normal-dispersion　(ANDi)　Yb-doped　mode-locked　fiber　laser,　in　which　nonlinear　polarization　rotation　(NPR)　is　used　to　realize　mode-locking　without　any　dispersion　compensation.　Based　on　the　coupled　nonlinear　Schrodinger　(CNLS)　equation,　a　model　simulating　the　mode-locked　process　of　an　all-normal-dispersion　ring　fiber　laser　is　developed,　which　shows　that　the　achievement　of　stable　mode-locking　depends　on　the　alignment　of　the　polarization　controller　(PC)　along　the　fast-polarization　axis　of　the　fiber,　the　birefringence　intensity,　and　the　net　cavity　dispersion.　According　to　the　theoretical　analysis,　stable　mode-locked　pulses　with　pulse　duration　300　ps　and　average　output　power　33.9　mW　at　repetition　rate　36　MHz　are　obtained.