The invention relates to an arc fault detection method and a protection device. The arc fault detection protection device comprises a current transformer, an I/V conversion circuit, a rectifying circuit, an integral circuit and a microprocessor, wherein the I/V conversion circuit, the rectifying circuit, the integral circuit and the microprocessor are connected in sequence. The current transformer detects current signals of a protected circuit, current signals are converted into voltage signals through the I/V conversion circuit arranged at the secondary side of the current transformer, the voltage signals are sent into the rectifying circuit to be rectified through a voltage follower, wave signals obtained after rectification are provided for the integral circuit, the integral circuit provides the voltage level cumulant in a preset time period for the microprocessor, the microprocessor captures the periodical integral value through timing A/D conversion and stores the periodical integral value, the current waveform change of the protected circuit is detected through an arc fault detection algorithm, arc fault judgment is conducted, disturbance caused by arc fault, or caused by normal starting of a load or caused by power regulation can be effectively distinguished, mistaken disengagement actions of the device can be reduced, and reliability is higher.