The radial variation of sap flow density is a prerequisite for accurate estimation of whole tree water use and ignoring this radial variation will lead to considerable error in estimation of tree water consumption. Based on the thermal diffusion probe method, the sap flow density of 11-aged Eucalyptus urophylla × Eucalyptus Grandis was continuously monitored at the sapwood depth of 0 ~ 2cm, 2 ~ 4cm and 4 ~ 6cm in Guilin Botanical Garden for 32 days during the growing season in 2021. The results showed that the diurnal variation of sap flow density in each sapwood depth showed a single-peak pattern, and the sap flow density decreased with the increase of sapwood depth. The apparent radial variation of sap flow density appeared in Eucalyptus urophylla × Eucalyptus Grandis with middle-class diameter, and it will lead to a large error in estimating whole-tree transpiration if not considering this radial variation. The data set can provide basic data support for analyzing the radial variation of sap flow density of eucalyptus and comparing the difference in the radial variation pattern of sap flow density among various tree species.