A clear definition and a very fine classification of the unmanned undersea vehicles are given in this paper. Following a brief introduction of the advances on the unmanned undersea vehicles the paper points out that the autonomous underwater vehicles at present is a hot spot in the research realm of the unmanned undersea vehicles. This paper describes the research and development achievements pertinent to the unmanned undersea vehicles in Shenyang Institute of Automation (SIA), Chinese Academy of Sciences with the cooperation of organizations home and abroad in the last two decades. SIA started to be engaged in the research and development of the remotely operated tethered vehicles in the end of 1970's. This paper gives a wide introduction of the critical characteristics and technical descriptions of the first remotely operated tethered vehicle “HR- 01” in China, the first autonomous underwater vehicle “Explorer” and the autonomous underwater vehicle CR-01 (6 000 m).