Abstract: A grounding grid breakpoint diagnostic method for a transient electromagnetic method, based on a transient electromagnetic detection apparatus. The method comprises: (101) disposing a test line at a position above a grounding grid to be diagnosed on the ground, and determining coordinates of a detection point; (102) obtaining information about coordinates of the detection point, and coinciding the center of the transient electromagnetic detection apparatus with the coordinates of the detection point; (103) performing, by the transient electromagnetic detection apparatus, measurement along the test line point by point, so as to obtain measurement data; (104) processing, by using diagram forming software, the measurement data to form a longitudinal resistivity cross-section diagram of the detection point according to a preset formula; (105) determining whether a breakpoint occurs at the detection point according to the longitudinal resistivity cross-section diagram.