The liquid crystal phases are postulated as a mechanical rotor-bearing system in which liquid crystal molecular core and terminals are estimated as the rotor and axes, respectively, the terminals also function as molecular rotors in the subsequent layers. Some general rules are proposed that relate phase stability to molecular structures and the mechanical rotor-bearing model is applied to explain the phase behaviors. Phenomena of the thermal stability of phase and phase transition are explained in terms of basic mechanical and dynamical parameters: center of gravity, eccentricity, moment of inertia and mass distribution. Fluorination effects on liquid crystallinity are explained in a uniform manner by mechanical and dynamical basis. Moreover, we have also examined interesting liquid crystalline systems such as liquid crystal oligomers. Characteristic thermal behaviors are correlated to the molecular structures and their mechanical or dynamical parameters to complete validity of the model proposed.