Abstract: In determining turbine efficiency, the thermodynamic method obtains turbine discharge and efficiency through measuring specific energy per unit, with no direct measurement of discharge, but its accuracy is affected significantly by uneven velocity profiles at low-pressure sections. Focusing on this problem, this paper presents an improved iteration procedure to determine flow velocity at low-pressure sections, discharge and efficiency. It saves test work due to avoiding direct measurement of flow velocity.In the calculation procedure, we iterate the corrective terms of specific mechanical energy and flow velocity at the low-pressure sections, and obtain a final velocity that better represents the mean flow velocity at the low-pressure sections, so that the resulted efficiency is more accurate than direct measurement. Test results show that specific mechanical energy, turbine discharge and efficiency can be worked out by only several iteration steps, which can meet engineering test requirements, demonstrating the procedure is an improvement on the application of the thermodynamic method to low-head turbine measurements.