Abstract: ‍ ‍Distributed underwater wireless sensor network （UWSN） is a compelling approach for underwater target exploration， and its main objective is underwater distributed detection. Due to the limitations of large propagation delay and narrow available bandwidth in underwater acoustic data transmission， which make it intractable to handle real-time transmission of raw data collected by underwater acoustic array， and the poor performance of existing distributed quantization detection methods under low signal-to-noise ratio， we propose a multi-bit quantization detection method based on locally most powerful test （LMPT） in non-ideal channel scenarios. Firstly， by combining the fading characteristics of underwater acoustic channel and the transmission error characteristics of coding channel， the UWSN weak signal detection model with non-ideal channels is conceived and further transformed into an asymptotic one-sided hypothesis test problem； Secondly， the locally most powerful detection method based on multi-bit quantization is derived， and its false alarm probability and detection probability are theoretically analyzed. Then， the problem of multi-bit quantization threshold optimization based on LMPT in non-ideal channels is proposed， and the detection performance loss introduced by quantization is investigated. Finally， the effectiveness of the proposed methods and related theoretical analysis is verified by the simulation results.