A　low-noise　narrow-linewidth　distributed　Bragg　reflector　(DBR)　single　frequency　1.5-mu　m　fiber　laser　with　a　complex　optical-feedback　loop　(COFL)　is　demonstrated.　The　COFL　is　used　to　reduce　the　relative　intensity　noise　(RIN)　and　narrow　the　linewidth,　which　is　composed　of　an　erbium-doped　fiber　amplifier　(EDFA),　an　unpumped　Er80　fiber　and　a　sagnac　loop　mirror.　The　COFL　combines　the　nonlinear　amplification　effect　of　saturated　optical　amplifiers,　the　standing-wave　saturation　effects　of　saturable　absorber　(SA),　and　the　self-injection　locking　technology　at　the　same　time.　The　effects　of　self-injection　locking　give　a　sufficient　proof,　which　the　RIN　is　reduced　and　the　resonance　peak　shifts　to　lower　frequency.　The　RIN　of　low　frequency　is　greatly　reduced　by　the　EDFA.　In　addition,　the　SA　narrows　the　linewidth.　After　the　COFL　suppression,　the　RIN　of　relaxation　oscillation　is　reduced　by　24.5　dB　from　80.3　dB/Hz　at　219　kHz　to　104.8　dB/Hz　at　87　kHz.　Furthermore,　the　linewidth　narrows　from　7.47　kHz　to　720　Hz.　Even　after　two-stage　fiber　amplification,　the　RIN　does　not　increase　significantly,　and　a　spectral　linewidth　well　below　1.8　kHz　is　also　achieved　at　the　output　power　of　11.1　W.