AbstractTo avoid the computational complexity and the mismatching between the results and qualitative analysis by using regression analysis, the method of grey relational analysis is selected after methods comparing to analyze the relation between piezometer water level and its influencing factors and estimate the height of the saturation line for a sluice in the Lower Yellow River. The concepts of degrees of grey incidence are discussed in detail to show how to determine which factors are the most important for the dependent variable and their orders. An example given in the paper indicate that the grey relational analysis is effective to extract the important factors for piezometer water level, and the results show that the grey incidence orders which show that the water level of downstream of that very day is critical for the piezometer water level of the sluice.