The traditional Lamb wave structure health monitoring imaging method based on reference signal is affected by environmental factors such as temperature change. To solve this problem, considering the difference in the scattered fields generated by the interaction between ultrasonic waves and defects in the reverse path, a Lamb wave imaging method is proposed in this paper based on the difference signal of sparse array in inverse path. Numerical simulations are carried out to determine the generation conditions of difference signal in inversion path, and the influences of the angles and distances between the defect and the two sensors on the amplitude of difference signal in inversion path. It is found that the difference signal in reverse path is much more obvious when the defect appears as asymmetric distribution towards the excitation sensor and receiving sensors; the amplitude of difference signal in inverse path is affected by distance difference of the Lamb wave propagating in reverse path and the scattering coefficient of the defect. On this basis, the effectiveness of the Lamb wave imaging method based on the difference signal in inverse path is studied numerically and experimentally. The results show that the Lamb wave imaging method based on the difference signal in inversion path can perfectly eliminate the interference between direct wave and the boundary reflection wave, and the imaging method can detect the defect at different positions in the plate. Moreover, the imaging resolution is higher and the defect location is accurate. The research work provides a new feasible scheme for the extensive health monitoring of plate structure.