Firstly, Erbium-doped fiber amplifier (EDFA) served as pre-amplifier may distort Brillouin gain spectrum (BGS) in coded Brillouin optical time domain analysis sensor. Here, we found that the EDFA has negligible impact on the shape of Brillouin phase spectrum (BPS). Experimental results show that a ∼5.4 MHz Brillouin frequency shift error caused by EDFA has been avoided by using BPS instead of BGS. Secondly, after eliminating phase fluctuation caused by optical fiber, the combination of Golay coding and coherent de…