The invention provides a lead screw thread bottom hardness micro-magnetic nondestructive detection method and belongs to the field of nondestructive detection. Two pole shoes of an electromagnet of a micro-magnetic probe are attached to two adjacent crests of a lead screw to form an excitation loop, by means of sine wave signal driving electromagnets with amplitudes increasingly strong scanned and at different frequencies, the thread bottom portion is periodically magnetized in an increasingly strong mode, and a detection coil making contact with the surface of a thread bottom receives Barkhausen noise signals in the periodical magnetizing process. Feature parameters including peak, half peak width and root-mean-square are extracted, a sine wave amplitude change curve of the feature parameters along with scanning is obtained, and finally Barkhausen noise signal feature parameters on sine wave amplitude values and the slope of the change curve of the feature parameters are scanned at different frequencies for hardness representation. During continuous detection, the micro-magnetic probe runs along with the rotary lead screw to finish hardness detection of the thread bottom of the whole lead screw. The method achieves quick nondestructive detection of the thread bottom of the lead screw, and the defect that a traditional hardness detection method can only conduct destructive sampling type detection is overcome.