Ultrasound imaging technique is applied to river model test in recent years, but the imaging features and inner relationships of sediments are still waiting for further study. This paper proposes some new relationships between B-mode ultrasound imaging signals and suspended sediment concentrations (SSC) after kinds of model experiments are conducted in a glass flume. And the influences of particle size, sediment material, ultrasonic frequency and flow velocity on the relationships are discussed in practical applications. Results show that the imaging area concentration (IAC), gray area concentration (GAC) and gray energy density (GED) of sediment imaging signals increase with the addition of sediments until images are filled with imaging signals. The GAC is the best one because of the widest variation range and better sensitivity when compared with the IAC. The GED is the most sensitive to the change of SSC, but it is easiest to reach saturation. The relationship between the GAC and actual SSC can be used to estimate unknown SSC and its vertical distribution when the concentration is below 4.0 ‰ with advantages of direct observation and real time.