The invention discloses a modularized device for removing NOx by synergy of large-area creeping DBD (dielectric barrier discharge) and a catalyst and belongs to the field of plasma technology application. The modularized device is characterized in that medium tubes sleeve linear ground electrodes which are grounded firmly, and array-type linear high-voltage electrodes are embedded into the linear ground electrodes to form a creeping discharge area; array-type wire-wire electrodes (1) are disposed in a discharge reaction chamber (2) to form a modularized discharge-removal device, and the modularized discharge-removal device and the catalyst are used for removing NOx synergistically; discharge plasmas are generated by excitation of a power system (4), and a matching system (3) is used for guaranteeing power output of a power source; an electrodiagnosis system (7) and an optical diagnosis system (8) are used for online diagnosis of large-area creeping DBD, a gas detection system (6) is used for diagnosis of treatment effects of NOx supplied by a gas supply system (5), and a catalyst characterization system (9) is used for catalyst characterization and studying plasma and catalyst synergistic mechanisms.