Terahertz Frequency Modulated Continuous Wave(THz FMCW) imaging technology has attracted extensive attention in the field of THz Nondestructive Testing(NDT) because of its high power, miniaturization, low cost, three-dimensional imaging and other characteristics. However, due to the limitation of microwave and terahertz devices, the terahertz signal bandwidth is difficult to expand, which restricts the range resolution of imaging. Although high carrier frequency can achieve large broadband, the accompanying low penetrability and low power will limit the application scenario of THz FMCW imaging system. Therefore, focusing on the field of terahertz wave nondestructive testing, this paper proposes a time-division frequency-division multiplexing 114~500 GHz ultra-wideband terahertz signal generation method, which is based on the quasi-optical design of multiband common aperture to achieve the common aperture of ultra-wideband signals. In addition, a multiband fusion algorithm is proposed to achieve effective fusion of ultra-wideband signals, and the range resolution is improved to 460 μm. The effectiveness of the system and algorithm is verified by artificially designed multilayer composite materials, and the high-resolution 3D imaging results of Integrated Circuit(IC) chips are obtained.