Abstract: Random wave dynamic response analysis method is studied and used to analyze a sample drilling jack-up unit. The result shows that current suppression on the dynamic and static responses of the unit increases as the current speed increases, but the dynamic amplification factor decreases meanwhile. The result also shows that the inertial force computed by random wave dynamic response analysis method increases relatively slowly since this method can take account of current effect. So random wave dynamic response analysis method should be selected to calculate dynamic amplification factor and inertial force under large current speed for optimizing structure design of legs and increasing variable deck load of jack-up units.