Abstract: The flow rate is the key parameter for evaluating the absolute efficiency of a hydraulic turbine. This paper reviews typical turbine flow measurement methods and studies the uncertainty evaluation for the ultrasonic transit time method. The total station was used to establish the accurate 3D model of the pipeline, and the geometric parameters were calibrated by measuring the relative position between the probe and the pipeline, then good uncertainty results were obtained. With a reasonable estimation of the ultrasonic transit time and flow rate integral modal, the uncertainty evaluation method for flow rates of super large calibers is given.