Discovery of theUpper Ordovician in the North China Craton and determination of its geological time has received considerable concerns. By verifying the previous records of conodont and graptolite in the top part of the Ordovician carbonate sequences at different localities, this study defined top of the Taoqupo Formation in Yaoxian County within the closure position (44973 Ma, the early Katian) of graptolite Diplacanthograptus spiniferus Biozone. This position represents the highest sequence of the Orvocician in North China. However, The Stratigraphic Chart of China (2014) placed the top of the Taoqupo Formation around the division line between Qiantangjiangian and Hirnantian Stages (4456 Ma), with the latter slightly higher than the end position of the graptolite biozone. The difference is evident and needs absolute age data. This study found one layer of bentonite at the lower part (about 5m to the bottom) of the Taoqupo Formation in Yaoxian. Geochemical data of bentonite samples reveal that they are potassiumrich feature (K2O＞Na2O), with K2O content of 381% close to the average value (475%) of 17 Ordovician bentonite samples from the southern margin of the Ordos Basin. Zircon LAICPMS UPb dating shows that the bentonite bed emplaced at 4537±33 Ma (MSWD = 025). Considering sampling sequences and relatively quick sedimentary rate of the limestone, it can be concluded that the bottom of the Taoqupo Formation is at 454 Ma (late Sandbian Stage). The age obtained in this paper is consistent with the previously obtained data, with deviation within the error range, indicating that the age in this paper is credible. Therefore, the bottom boundary of the Taoqupo Formation in The Stratigraphic Chart of China (2014) should shift downward appropriately.