Abstract: GPR has the characteristics of fast detection speed， strong penetrating ability and high resolution. It is an effective non-destructive detection technology and has a wide range of applications in municipal construction， transportation， security and other fields. Inversion of stratified medium parameters is a necessary step for imaging and detection of underground targets in GPR. In this paper， an inversion algorithm of layered media parameters based on curve fitting is proposed. Firstly， the RMS velocity of underground media was obtained by fitting the reflected wave curve in B-scan data and combining with the electromagnetic wave vertical incidence model. The relative dielectric constant and layer thickness information of layered media were obtained by inversion through DIX formula. Finally， the accuracy and effectiveness of the proposed algorithm were verified by finite difference time domain （FDTD） simulation software.