Limited by the diffraction limit, the theoretical limit of spatial imaging resolution for far-field terahertz imaging technology is half the wavelength, which fails to meet the testing requirements for the characterization of microscale information in materials. To address the application needs of micro-nano defect detection in new materials such as semiconductor materials and ordered structural materials, this paper designs a wide-bandwidth frequency-swept continuous-wave terahertz near-field imaging system. The system adopts an all-electronic integrated terahertz transceiver module, and through terahertz beam spatial synthesis, it achieves seamless coverage of the test frequency range from 0.11 to 1.10 THz with a frequency resolution of 1 Hz. Via multi-frequency point information fusion, micro-nano defect detection and identification in materials are realized, with a spatial imaging resolution of ≤100 nm, the imaging field of view reaches 100 μm×100 μm. Tests and characterizations on semiconductor materials and ordered structural materials verify that the system in this paper can obtain high-quality near-field images by selecting terahertz frequency points at which the test materials exhibit strong responses to the high-resolution frequency-swept continuous wave.