This paper describes s a new X-ray fluorescence technique for in situ determining concentrations of various elements in seabed sediments and, based on scattered radiation, advances a method for correcting the influence of water content of natural seabed sediments upon the results of X-ray fluorescence analysis. Tests show that this technique can perform the underwater analytical tasks at a depth of less than1000 meters and simultaneously determine more than10 elements at the detection limit of (10～200)×10^-6 without liquid nitrogen supply. The in situ X-ray fluorescence technique proves to be a rapid, economical and effective analytical method.