The key to the problem of probing the concentration of suspended sediment in water and its variation with eooustic equipment is how to calibrate the obtained data.Combining the acoustic backscatter intensity data with the real concentration of suspended sediment from water samples collected from the Changjiang Estuary,three in-situ calibration methods for ttansfomting measured sediment are induced.Results show that the discrepancies between calibrated values given by characteristic time calibration and real ones are less than the values given by single shot method,and the statistical error is 20% approximately.The calibration on characteristic times is practical and simpler than simultaneous calibration.