Abstract: To improve the detection performance of extended targets in shallow water, the model of extended target echoes coupled with shallow water acoustic channels is modeled using the shallow water acoustic channel model and the multi-highlight model. The theoretical results of replica correlation integration (RCI) detection for extended target echoes coupled with shallow water acoustic channels are provided. The RCI detection performances under different shallow water conditions are analyzed by simulation methods using the linear frequency modulation (LFM) waveform with the bandwidth being 50 Hz, 100 Hz, 500 Hz and 1000 Hz respectively. The results show that the sea depth, the sonar depth, the target position and the waveform bandwidth all have influences on the expansion characteristics and the RCI detection performances of shallow water target echoes. The suitable sonar depth and waveform bandwidth may improve the detection performance of extended targets in shallow water.