The principle of applying Ground penetrating radar (GPR) in target detection is based on the electrical parameters of medium, such as dielectric, conductivity and permeability. Its application mainly concentrates on the detection of medium interface and target shape. In theoretical study, the simulation model is built with homogeneous medium. But the medium is heterogeneous and random distribution in practice. When radar wave propagates in the heterogeneous medium, it will produce scattering and diffraction at electrical interface and makes the radar wave seriously distort, the amplitude of received wave is also changed. It has influence on the resolution and detecting depth. In this paper, we build the stochastic model with normal distribution function and use high order FDTD method to simulate the GPR signal response, then analyze wave characteristics and target response in different random models. The results demonstrate that the random heterogeneous media model could describe the practical detection environment. It has the extensive applicability and lays a foundation for the parameters of medium extraction and data inversion.