High voltage direct current (HVDC) power transmission is one of the key development directions in China. Fast and accurate fault positioning of the HVDC transmission line is of great significance in ensuring operational reliability of the HVDC system and reduce shutdown time. The main technologies for fault positioning of an HVDC transmission line and flexible DC grid, including wave distance ranging, inherent frequency, fault analysis and the non-synchronous fault location method, are introduced and analyzed. The advantages and disadvantages of different fault positioning technologies are discussed. Finally, the future development of HVDC transmission lines is discussed by combining with the development trend of sensor, computer and artificial intelligence technology. This paper should provide a good reference for researchers working on fault positioning methods for HVDC transmission lines. This work is supported by the National Key Research and Development Program of China (No. 2018YFB0904700).