Soil detachment capacity is the maximum soil detachment rate when sediment concentration of overland flow is zero. It is the foundation of the determination of rill erodibility and soil critical shear stress, and wide application of the process-based soil erosion models. A detailed analysis indicated that runoff plot could not be used to measure soil detachment capacity by overland flow. The potential effects on soil detachment capacity and their mechanisms were fully discussed in the aspects of the type and size of hydraulic flume, representation of soil sampling, length of soil sample, disturbance of soil sample, initial soil moisture, and duration of flowing water scouring. The uncertainties in soil detachment capacity measurement were systematically analyzed. This paper is helpful to understand the dynamic mechanism of soil erosion processes, and to choose the rational methods and experimental procedures to measure soil detachment capacity by overland flow.