Dual AGNs with sub-kpc separations are hard to find with ground-based telescopes due to the limited angular resolution, but they are crucial for understanding the merging history of supermassive black holes and AGN triggering. In recent years, spectroscopic searches such as those using the Sloan Digital Sky Survey have made significance progress in identifying dual AGNs at z < 0.5, but rest-frame optical spectroscopy is still too expensive for large samples of AGNs at high redshift, where galaxy mergers are thought to be more common. We employ a new astrometric technique to find unresolved dual AGNs at high redshift in time-domain imaging surveys. The technique includes two complimentary methods: variability, which detects the centroid shift because of the non-synchronous variation of two AGNs, and color, which measures the centroid shift between two different filters due to the color difference of two AGNs. The technique is suitable for time-domain imaging surveys such as the ongoing Dark Energy Survey (DES) and the Large Survey Synoptic Telescope in future. We will present our preliminary results based on DES 4-year data including some dual AGN candidates identified from astrometry.