Using FE analysis, this work fully devoted to added masses determination of the plate in infinite liquid in the case of different movements. Various forms and sizes of the plate are considered. The problem consists of two parts: first is studying of the plate motion in liquid as rigid; second is studying of the plate vibrations in its own modes, fixed with a hard screen and contacting with liquid by one side. The condition observance of liquid environment continuity leads to the Laplace equation, which is solved by using numerical approach. Finite element analysis of steady state problem is performed for added masses determination using thermal analogy. A compact analytical solution of the two considered problems is presented. The results of finite element analysis and corresponding analytical results of the problems are compared for the case of infinite liquid environment.