The invention belongs to the technical field of knife rest performance detection and discloses an online detection device for performance parameters of a numerical control knife rest. The problems that during current detection of performance parameters of a knife rest, it is needed to manually switch sensors, and the detection efficiency is low are solved. The online detection device for the performance parameters of the numerical control knife rest comprises a servo knife rest, an installing platform and a knife rest performance parameter online detection device; the knife rest performance parameter online detection device is composed of a knife rest detection device body and a vibration sensor automatic replacing device; the knife rest detection device body comprises a knife disk positioning precision and knife changing speed detection device, a knife disk vibration detection device, a knife rod vibration detection device, a knife rest running noise detection device, a knife rod deformation detection device, a centering performance detection and adjustment module and a synchronous rotation module; and the vibration sensor automatic replacing device comprises electromagnetic clamping claws, a servo motor and a worm gear and worm rotation table. According to the online detection device for the performance parameters of the numerical control knife rest, sensors for detection are designed onto the complete online detection device and are adjusted according to different knife rests, installing is convenient and flexible, and adaptability is high.