1. A method for three-dimensional polarization-based confocal microscopy, comprising the steps of: providing a light source for emitting a beam; enabling the beam to pass through a first linear polarizer and an optical grating containing a structured pattern so as to generate a linear-polarizing structured light, wherein the optical grating is coupled to a linear driver which is coupled to a control module, and thereby, controlled by a signal provided from the control module for driving the optical grating to perform at least one-dimensional linear displacement movement so as to change a position of the optical grating and thereby shift the linear-polarizing structured light during the one-dimensional linear displacement movement; projecting the linear-polarizing structured light onto a surface of an object so as to form a plurality of beams containing focus information; performing a vertical scanning process upon the object; capturing the plurality of beams containing focus information during the vertical scanning process so as to form a series of images by a linear-polarizing imaging module; and analyzing the series of images for reconstructing a surface profile of the object.