The problem of non-destructive evaluation and testing of road quality using mi- crowave radar system is considered. Performance of two types of radar system was studied numerically with FDTD modeling: the system with a single antenna, and the system with two horn antennas. Numerical analysis shows the general ability of microwave radar system to detect thin water layer between asphalt and concrete layers. The details of implementation of the radar system and their influence on the performance are discussed in the paper.