Abstract: In Ground Penetrating Radar (GPR) applications such as detection of targets located in layered medium, the time-domain Back Projection (BP) imaging algorithm is a commonly used imaging technique. However, the heavy computation burden and low-quality imaging results limit the practical application of this algorithm. This paper presents a new Fast Back Projection (FBP) high-resolution imaging method. Firstly, a new fast time-delay calculation method based on one-dimensional search operation or a quadratic equation solving operation is presented. Secondly, a new method to improve the quality of imaging results by using weighted factor is presented and a typical weighted factor is designed. Through processing simulation data, the FBP imaging results show that the algorithm can be applied effectively to the target imaging embedded in two layered medium.