In recent years, with the progress of science and technology, underwater detection technology has provided great convenience and security for offshore and river outdoor fishing activities. Sonar fish detector is a kind of auxiliary accessory to observe the fish condition. It is suitable for fishing enthusiasts and fishermen to fish in rivers, lakes, seas and other places. It can help users to easily judge the weather temperature, water depth, fish or fish number and depth. The research on the detection mode of sonar fish detector can provide an effective basis for improving the function of the equipment and optimizing the detection effect.