The exploitation of blue polymer emitters is of great importance for the application of solution-processed organic light-emitting diodes (OLEDs) in full color display. The highly efficient blue thermally activated delayed fluorescence (TADF) polymers are rarely reported up to now. Herein, we report an efficient approach to construct blue TADF polymers by ring-opening metathesis polymerization (ROMP) of norbornene. By side-chain engineering strategy, the polymers are endowed with distinct TADF features. By use of these blue polymeric emitters, the nondoped OLEDs achieved a maximum external quantum efficiency of 7.3% with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.20, 0.29), which represents the state-of-the-art device performance for the TADF-based blue polymer light-emitting diodes (PLEDs).