A new land coupled data assimilation (LCDA) system based on the four-dimensional ensemble variational (4DEnVar) method is developed and applied to the fully coupled Energy Exascale Earth System Model version 2 (E3SMv2). Monthly mean soil moisture and temperature analyses from a global land reanalysis product are assimilated into the land component of E3SMv2 with a one-month assimilation window along the coupled model trajectory from 1980 to 2016. The LCDA system yields improved simulation of soil moisture and temperature compared with the control simulation, with improvements found throughout the soil layers and in many regions of the global land. Furthermore, significant improvements are also found in reproducing the time evolution of the 2012 U.S. Midwest drought, highlighting the crucial role of the land surface in drought lifecycle. It is noteworthy that the climate variabilities in the North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) index are realistically captured by the coupled land data assimilation. These findings motivate further research to systematically evaluate the contributions of land surface states to subseasonal-to-multidecadal climate variability.