Abstract: When the pulsed eddy current technology is used to detect the wall thickness of pipelines with coating, the large lift-off caused by the coating will change the detection signal, thus affect the change law of the signal characteristics and reducing the detection accuracy. In order to solve this problem, through the analysis of the relationship among the 3 factors, namely, the characteristic value of the late signal slope, the lift-off height and the pipe wall thickness, it is found that the late signal slope value obtained under different lift-off height has a a one-to-one relationship with the pipe wall thickness. Therefore, a wall thickness inversion method based on surface fitting is proposed, and then, the pipeline test pieces are used for experimental verification. The results show that the inversion error of pipe wall thickness with coating layer can be controlled within 7%, indicating that the method has extensive engineering application value.