The invention discloses an electromagnetic ultrasonic detection method for surface defects, belongs to a non-destructive testing technology, and aims at solving the problem that the defection accuracy is affected by change of a lift-off distance in an existing electromagnetic ultrasonic detection method. The method comprises the following steps: changing the lift-off distance of an electromagnetic ultrasonic sensor detection probe; measuring signals of standard samples at different lift-off distance, and carrying out signal treatment to obtain the lift-off slope; building a corresponding fit function by the relationships between the lift-off slope and the defect depths at different defect depths; and substituting the lift-off slope obtained by detecting the to-be-detected defects into the fit function, so as to achieve the purpose of quantitative detection of the defects. The electromagnetic ultrasonic detection method for surface defects is simple and feasible. Compared with an existing method for detecting the defects by peak strength and transmission coefficients, the effects on the lift-off distance of the detection probe can be reduced; and measurement on defect-free detection signals at the same lift-off distance in the detection process is avoided.