Abstract：The geometric meaning of mathematical expression which describes a line segment on ground surface before and after crustal deformation is analyzed, it is pointed out that translation, rotation and strain are three elements of combinational crustal deformation. For distinguishing the tidal tilt belong to which one of three elements, the geometric and physical meaning of tidal tilt are analyzed.On the basis of the analysis the observations of tilt earth tide on the eastewestern and northsouthern directions which can determine the amount and the direction of the generating tide force and the analysis on each component of tidal strain tensor,it is found that there is mathematical relation between components of tidal tilt and shear strains related to radius of earth and thus tidal tilt possesses shear property.
