Deep-blue organic light-emitting diodes (OLEDs) with both high efficiency and stability remain exclusive in scientific literatures after decades of research. A key reason is the chemical bond dissociation through conical intersections between potential energy surfaces (PESs) of energetically-hot excited states and dissociative states. Here, we report a deuteration strategy to stabilize blue thermally activated delayed fluorescence (TADF) emitters. It is unveiled that deuteration would lower high-frequency vibrations to create shallower PESs in both ground and excited states, energetically retarding the cross of the conical intersection point in dissociative process and alleviate vibrational coupling to eliminate nonradiative decay. With a deuterated blue TADF compound, namely 2,3,4,5,6-pentakis(9H-carbazol-9-yl-d8) benzonitrile, as the sensitizer, a deep-blue OLED simultaneously achieves a peak external quantum efficiency of 30.3%, a Commission Internationale de L’Eclairage coordinate y value (CIEy) of 0.17, and a superb LT80 (time to 80% of initial luminance) of 227 h at 1000 cd/m2. And a blue OLED with a CIEy~0.19 shows an even longer LT80 of 456 h at 1000 cd/m2.