The invention belongs to the technical field of nuclear fuel component detection, and relates to an online detecting device and method for surface [alpha] pollution of a MOX nuclear fuel rod. The online detecting device comprises a signal acquiring, adjusting and processing unit, a glove box, and a detector and a driving device disposed in the glove box, wherein the detector is used for detectingthe pollution of the surface of a nuclear fuel rod passing therethrough; the driving device is used for driving the nuclear fuel rod into and out of the detector; the signal acquiring, adjusting and processing unit is used for acquiring, adjusting and processing the pollution signals of different areas of the surface of the nuclear fuel rod detected by the detector. The online detecting device andmethod can achieve the related operations in the glove box, can detect the [alpha] contamination of the 100% surface of the MOX nuclear fuel rod under remote control, and can accurately calculate the[beta] pollution level of the surface of the nuclear fuel rod and the total quality by nuclear parameters obtained by the detecting device according to the material characteristics of the MOX nuclearfuel rod.