Contactless power transfer (CPT) technology can make electrical equipment get rid of the shackles of wires, can greatly expand the scope of the electrical equipment, and enhance the safety performance of power supply in special environment. Aiming at the inductive contactless power transfer (ICPT) technology which is one of CPT technology widely used, firstly, the development of the ICPT technology is discussed. And then, using the Poynting vector theory, the principle of CPT technology is discussed. The existing CPT technology is classified according to the difference of the realization principle. The magnetic resonance contactless power transfer (MRCPT) technology is classified into ICPT technology. The main technical difficulties of ICPT technology are analyzed systematically. It is pointed out that the low coupling coefficient of coupler is the key technical problem of ICPT technology, and the other problems are caused by this problem. Finally, the key technologies of ICPT system and the existing solutions are discussed.