Abstract: The conventional batch synthesis system suffers from limited mass and heat transfer efficiency, leading to multiple side reactions during the preparation of bisphenol A-aniline-based benzoxazine monomer (BA-a) and making it difficult to improve the ring-closed ratio (η). To address this issue, a continuous-flow microreactor system was constructed, enabling controllable regulation of η. Under the optimized conditions of 120 ℃ and a residence time of 15 min, a product yield of 62.3% and a ring-closed ratio of 96% were achieved, demonstrating superior overall performance compared with the traditional batch method (78 ℃, 5 h, yield of 55.1%, ring-closed ratio of 94%). Mechanistic analysis indicates that lower temperatures or shorter residence times result in incomplete conversion of reactants, whereas temperatures above 130 ℃ and residence times longer than 20 min promote ring-opening side reactions of the oxazine structure. Through the synergistic control of temperature and residence time, efficient conversion can be achieved while effectively suppressing side reactions. The self-catalytic effect of phenolic hydroxyl groups accelerates the curing kinetics of samples with a ring-closed ratio of 91% within the temperature range of 100—120 ℃. With increasing ring-closed ratio, both the dielectric constant and dielectric loss of the materials continuously decrease, reaching minimum values of 2.92 and 0.0128, respectively. After immersion in 3.5% (mass fraction) NaCl solution for 15 d, sample with the high ring-closed ratio (η=96%) still maintains an impedance of about 400 MΩ·cm², exhibiting excellent dielectric properties and corrosion resistance.