Abstract: On the basis of high speed films of moving arc taken in quantity during underwater cutting and oscillograms of arc current and voltage, this paper analyses the characteristics of the burning of arcs in consumable electrode water jet semiautomatic underwater cutting, studies its mechanism and advances the hypothesis that there may exist a high-temperature "gas cavity" during continuous steady cutting. This paper also deals with the requirements to the power sources for cut ting and discusses the most important problems in developing cutting apparatus. The relationship among differen parameters has been obtaind through technological experiments carried out in continuous steady cutting condition. The performance, characteristics and principal technical datum of GSS-800 consumable electrode water jet semiautomatic underwater cutting apparatus are also outlined. The last part of the paper is a brief account of a successful cutting on site at a depth of 60 metres under water, employing the new consumable electrode water jet technique with a cutting speed up to 20m/h and more.