Abstract: Additional dynamic loading generated by wire rope swinging due to waveinduced motion of the crane vessel adversely affects its buoyancy and stability. A hydrodynamic model of revolving crane vessel “LANJING” was built to calculate the motion response in irregular waves. Spectral analysis was employed to calculate the motion transfer functions from fulcrum of suspension to lifted object and the statistic characteristic value for lifted object motion. Characteristic value for additional dynamic loading, whose influence on buoyancy and stability of the crane vessel was also analyzed in this study, was obtained according to different waves, rotation angle and rope length.