Comprehensive SummaryMolecular weight distribution (MWD) is fundamental for polymer analysis, which influences many important properties of polymeric materials. In this work, we demonstrate the development of a computer‐aided droplet‐flow system that combines photo‐mediated reversible‐deactivation radical polymerization (RDRP) and chain transfer agent (CTA) diffusion strategy to enable facile MWD control for the first time. Synthetic advantages of this photo‐flow polymerization allow controlled chain‐growth to yield a variety of polymers of tunable MWDs in a broad range (Ð ≈ 1.1—1.9) with predetermined molecular weights (Mn ≈ 4—30 kDa) and good chain‐end fidelity. Notably, the computer‐aided platform has streamlined an automatic and high‐throughput pathway to prepare polymer libraries of tunable MWDs. For copolymers, chemical compositions could be readily regulated besides MWDs with the droplet‐flow platform. We believe that this work should be attractive for polymer engineering, and informative to create more flow polymerization techniques toward on‐demand control of diverse polymer characters.