In the light of the principle that elevations should be identical at the same water level, it is held that the potential base equivalent elevation which has the same meaning as the potential base ought to be used in the designing and construction of water conservancy projects. Calculation shows that the difference between the currently used elevation and the potential base equivalent elevation is as large as 7 m along the same measuring line with latitude difference 12° and altitude difference nearly 2500 m. Such a large deviation should not be neglected. This paper also puts forward some opinions on the arrangement of gravity points in elevation measurement and the precision of gravity interpolation.