This paper proposes an improved intrusive generalized polynomial chaos expansion (gPCE) method for uncertainty quantification (UQ) in ground penetrating radar (GPR) modeling. The uncertainty in simulation results induced by the uncertain parameters of dispersive and lossy soil is quantified with the auxiliary differential equation (ADE) finite-difference time-domain (FDTD) method combined with gPCE. To avoid the curse of dimensionality in modeling complex systems

the combination of uncertainties is incorporated into the new method to evaluate the interval of the uncertainty of the output. The results from the new method are compared against traditional UQ method Monte Carlo method (MCM). The new method shows its considerable advantage in the computational expense and speed.