The so-called Millennium Eruption of Baitoushan Volcano is one of the largest of the Common Era but its date has been uncertain. Recently, Oppenheimer et al. (2017) reported the eruptive year as late AD 946 using a new method called carbon-14 spike matching. However, it is necessary to verify their result to confirm the eruptive year, since only one wood sample was used in their study. We verified the eruptive year by measuring 14C contents in tree rings from another wood sample buried during the Baitoushan eruption. We succeeded in reproducing the AD 774–775 14C spike (Miyake et al. 2012), and counted the number of rings from the outermost ring accompanied by bark to the ring possessing the AD 774–775 14C spike. We found the outermost ring was formed in AD 946. Our study supported the result of Oppenheimer et al. (2017), which makes the eruptive year conclusive. Also, we suggest that the 14C spike-matching method can be a prominent dating tool applicable to ancient woods that are difficult to date using the usual dendrochronology techniques.