Abstract: Through-wall imaging techniques with Ultra-WideBand (UWB) radar are promising candidates for non-destructive detection, especially in disaster areas like calamity rescue scenarios, counter-terrorism and so on. These applications always require high-resolution target imaging to identify the object shape. Based on this requirement, a complex target boundary imaging algorithm for UWB radar is proposed to realize the shape estimation and identification of the target behind walls. As the application is a near field problem, the algorithm offsets the influence from walls using the incident angle of the radar echo calculated by the time-delay difference curve, and estimates the target boundary effectively. Simulation and experimental results of targets behind walls with different shapes show that the proposed algorithm can remove the influence from walls, estimate the target boundary effectively and realize the basic target identification.