The invention relates to a marine drift diameter gauge type drill rod or oil pipe leakage flux detection device and method. The marine drift diameter gauge type drill rod or oil pipe leakage flux detection device is provided with a fishing head and a drift diameter gauge, wherein the drift diameter gauge comprises an excitation coil and a signal acquisition and emission device; the excitation coil is electrified by a lithium battery; the excitation coil is electrically connected to the signal acquisition and emission device; a permanent magnet is arranged between the fishing head and the drift diameter gauge; the magnetic field of the permanent magnet is contrary to the magnetic field of the excitation coil; and the signal acquisition and emission device comprises a leakage flux sensor, an amplification filtering circuit, an A/D (Analog to Digital) conversion circuit, a coder and an electromagnetic wave emitter and is used for acquiring and transmitting flaw signals. The marine drift diameter gauge type drill rod or oil pipe leakage flux detection device has the beneficial effects that the online detection of an oil pipe or a drill rod is realized, the flawed drill rod or the flawed oil pipe is timely rejected; the additional operation cost resulting from drilling troubles caused by descending a well is avoided; and the drill rod or the oil pipe does not need to be transported to the land for detection.