Ultra-wideband (UWB) microwave imaging technology can be used as an effective method of detecting early breast cancer, which is based on the difference of the electrical characteristic between normal breast tissues and tumor. The method can provide both the sufficient resolution and the adequate penetration depth in the breast. In this paper, the finite difference time domain method is employed to simulate the microwave propagation in three-dimensional breast tissue. The single pole Debye model is used to approximate the real electrical properties of the breast organism. The antenna arrays made up of 8 emitters and 9 detectors are performed for the detection. The confocal imaging algorithm is employed for the reconstruction of the breast tissue and location. The tumor information displayed in the reconstructed breast image verifies the correctness of the confocal imaging algorithm and the effectiveness of the UWB microwave imaging technique applied to the early breast cancer detection.