Abstract: Based on the principle of echo detection, a method of monitoring inland ships by sonar is studied in this paper. A ship draft detection system by using side-scan sonar is installed in Xijiang channel in Guangxi, and a large amount of monitoring data is obtained. By analyzing these data, the differences between ship targets and pseudo targets such as fish swarm, fishing net and garbage floating objects are studied, and the energy variation characteristics and linear structure characteristics of ship targets are summarized. According to these characteristics, a fast recognition method for ship targets is proposed. Finally, experiments show that the proposed method has the advantages in high detection rate, low false alarm probability and good real-time performance. This method provides a technical means for further realizing the intelligent monitoring of the navigation state of inland ships.