Objective To explore changes in the capacity and working efficiency of divers performing deep saturation dives at various depths.Methods The divers completed the specified underwater operations at the depths of 70 m,255 m and 493 m,and changes in their working efficiency were assessed by working time and errors occurred during the underwater operations.Results The time consumed for the joining up of flanges,the binding and measurement of underwater objects at the depth of 255 m all significantly prolonged,when compared with the time used at 70 m(P <0.05).The time used for the joining up of flanges,the binding of underwa-ter objects at the depth of 493 m did not prolong significantly,when compared with the time spent at 255 m(P <0.05).However,the time used for underwater measurement prolonged significantly(P <0.01)and the rate of error both in the joining up of flanges and meas-urement of underwater objects increased significantly (P <0.05).Conclusion In deep saturation dives,the capability and working ef-ficiency of divers all considerably reduced.The greater the depths were,the more significantly their operating dexterity and short-term memory were affected.