1. A method of comparing similarity of a 3D reference object and a 3D target object, the method comprising: providing a stereo camera; calibrating the stereo camera; a right camera of the stereo camera capturing a right image of the target object on a measurement surface; a left camera of the stereo camera capturing a left image of the target object on the measurement surface; generating a disparity map through 3D information obtained by the stereo camera; acquiring the target object from either the right image or the left image through background difference; utilizing the disparity map to calculate width, length and depth of the target object according to the right image and the left image; determining color characteristics of the target object; determining shape characteristics of the target object; selecting the 3D reference object for comparison with the target object; selecting a new 3D reference object for comparison with the target object if the length of the target object is outside a length threshold of length of the reference object; selecting the new 3D reference object for comparison with the target object if the width of the target object is outside a width threshold of width of the reference object; selecting the new 3D reference object for comparison with the target object if the depth of the target object is outside a depth threshold of depth of the reference object; selecting the new 3D reference object for comparison with the target object if color error between the color characteristics of the target object and color characteristics of the reference object is outside a color error threshold; selecting the new 3D reference object for comparison with the target object if shape error between the shape characteristics of the target object and shape characteristics of the reference object is outside a shape error threshold; and indicating a match between the target object and the reference object when the length of the target object is within the length threshold of the length of the reference object, the width of the target object is within the width threshold of the width of the reference object, the depth of the target object is within the depth threshold of the depth of the reference object, the color error between the color characteristics of the target object and the color characteristics of the reference object is within the color error threshold, and the shape error between the shape characteristics of the target object and the shape characteristics of the reference object is within the shape error threshold.