Rare earth element analysis had been carried out for the Taiyuan limestone and limestone water collected from the Renlou coal mine, and the results show that the total rare earth element (REE) contents of limestone are low and are 36.947×10-6 in average. The rare earth element patterns indicate that the LREE is rich and the HREE is depleted; the REE contents of limestone water are 0.0526×10-6 in average; the LREE and HREE both are rich; the fractionation between LREE and HREE is clear. The water-rock interactions in limestone aquifer had been studied, and the results indicate that the LREE content is stable, the fractionation of HREE is clear, and especially that of Y is a peak, the relationship between Y and Ca is positive correlation, the fractionation of Y/Ho, Y/Dy in limestone water is more obvious than in limestone. This paper considers that the peak effect of Y can be the distinguishing basis for limestone water.