Abstract: The seismic liquefaction discrimination is an important survey content in hydropower engineering and other fields. In relevant national codes, the standard penetration test(SPT) is recommended for liquefaction discrimination. However, the methods in these specifications are not fully applicable to the discrimination of the liquefiable layer of the dam foundation for dangerous old earth-rock dams. The main reason is that in water conservancy and hydropower projects, it is only pointed out that the measured SPT blow count and critical SPT blow count need to be corrected after considering the change of reservoir water level, but there is no relevant explanation on how to obtain the underground water level of the dam body for SPT blow count correction. The water level of the dangerous reservoir is generally lower than the normal pool level, and the buried depth of the groundwater level of the boreholes in the dam body is large, thus the measured SPT blow counts are large, and the calculated critical SPT blow count value is too small, and the liquefaction discrimination may be dangerous. Combined with the needs of practical engineering, this paper puts forward the rapid correction method of dam groundwater level. The main idea is to raise the water level in the hole(the maximum amplitude is the difference between the normal water level and the current water level), and then reduce the water level in the hole in combination with the elevation of the boreholes and the height of the dam. Finally, it introduces a series of correction studies of this method in some earth-rock dam safety appraisal projects, which is a supplement to the liquefaction discrimination for the current code, and has been well used in practical projects. The accumulated engineering experience can provide reference for safety assessment and reinforcement of nearly 20, 000 dangerous reservoirs in China during "the 14th Five-Year" period.