Studies on a high speed spindle variable preload technology have been largely conducted. Fixed position preload, constant pressure preload, convertible preload and variable preload methods have been used for the high speed spindle in machine tools. The previous studies performed by the author of this study were variable preload methods using centrifugal force and rubber pressure based on mechanical systems. In this study, a method that applies a variable preload to spindle bearings using various liquids is proposed. Also, the applicability of the proposed method is verified using an analysis on the method. In addition, the application of the proposed variable preload device to machine tool spindles is verified.