Abstract: As ship grounding accidents caused by “super draft”are increasing year by year, it is particularly necessary to measure draft of inland departing vessels by real time measurement. According to the characteristics of inland waterways and ships, a novel method for ship draft real-time measurement by using simultaneous scanning sonar is proposed. As the draft depth measurement benchmarks, the accuracy of water surface line is directly related to the final measurement accuracy, so firstly the water surface line extraction method based on statistical analysis is presented. Then the influence of sonar's size on output signals is deeply analyzed, and then the measuring principle is deduced. To prove these theoretical analysis results, the ship draft measurement system of a small scale is developed, and the tests are carried out at the same time. The results show that with the increase of ship speed, the measured error of the ship draft is of increasing tendency with the minimum error being -4. 2%, and the maximum -11. 4%. The test results prove the feasibility of the program, and also show a greater impact on the ship draft with the increase of ship speed. In the following reseaches on the influence caused by acoustic scattering, diffraction and other effects must be studied to improve detection accuracy.