The supporting data for the manuscript "Oxygen Isotope Compositions of Cellulose in Earlywood of Larix cajanderi Determined by Water Source Rather Than Leaf Water Enrichment in a Permafrost Ecosystem, Eastern Siberia". The data set includes relating meteorological data (i.e., temperature and precipitation from 1979 to 2015, and relative humidity from 2000 to 2016), soil amount from 1998 to 2015, and the data of δ18O values. The δ18O values' data include soil water from 1998 to 2015, stem water from 1997 to 2015, tree ring cellulose from 1981 to 2016, and daily monitoring of leaf water in 2014 and 2015.