By measuring the actual twist angle in the twist nematic liquid crystal cell and the surface torsional angle between the rubbing direction and the liquid crystal director at the substrate boundary, a new measuring method of the surface torsional anchoring energy for pure nematic liquid crystals has been given. The relation between the surface anchoring energy and the rubbing strength was studied. The intermolecular interaction between the polymer and liquid crystal is considered very important for the alignment of liquid crystals.