The helicopter time-domain electromagnetic (HTEM) method is a method that uses geophysical exploration technology and a helicopter platform to carry electromagnetic detection equipment. HTEM has developed rapidly, in both theoretical and technological terms, in recent years because of its high efficiency, ability to drape steep and variable terrain, large detection depth, and high resolution. This work briefly introduces the HTEM technology principle and forward and inversion theory, summarizes the main performance parameters of international representative HTEM systems, and analyzes the performance and structural characteristics of VTEM, SkyTEM and HeliTEM systems. To provide a technical reference for scholars engaged in HTEM instrument technology, we analyze the factors affecting the detection capability of HTEM systems and the main difficulties in system design. Taking China’s HTEM systems as the object of analysis, we introduce the key technologies behind the systems in detail, including high-power transmitting, receiving sensor design, and motion-noise-suppression technologies. This work also discusses the development trend of HTEM and the existing technical problems, including detection depth, measurement accuracy, and noise refinement classification, providing ideas for the further development of HTEM technology in the future.