1. A quick subpixel absolute positioning method, comprising the steps of: capturing a real-time speckle pattern of a target surface with an invariant speckle pattern-capturing device; providing a plurality of coarse-precision speckle coordinate patterns and a plurality of sets of fine-precision speckle coordinate patterns from at least one storage device, wherein the coarse-precision speckle coordinate patterns correspond to the sets of the fine-precision speckle coordinate patterns, respectively, and each fine-precision speckle coordinate pattern of each set of fine-precision coordinate pattern includes a coordinate value; and comparing the real-time speckle pattern with the plurality of coarse-precision speckle coordinate patterns by an algorithm of a data processing device to select one of the coarse-precision speckle coordinate patterns, and then comparing the real-time speckle pattern with the set of fine-precision speckle coordinate patterns corresponding to the selected coarse-precision speckle coordinate pattern to select one of the fine-precision speckle coordinate patterns and use coordinate values of the selected fine-precision speckle coordinate pattern to position the real-time speckle pattern, wherein the selected fine-precision speckle coordinate patterns are obtained when the selected coarse-precision speckle coordinate pattern is captured again and then captured repeatedly according to a fixed fine-precision displacement distance, wherein relationship between the fine-precision displacement distance and subpixels is defined below: 
 δ= M×Δ′ 
 P=η/δ 
 Δ′=η/ MP δ: a fine-precision displacement distance of a pattern M: magnifying power of an imaging lens of an invariant speckle pattern pattern-capturing device Δ′: a fine-precision displacement distance of an object η: size of pixels of a sensor P: number of cuts; wherein the coarse-precision speckle coordinate pattern is disposed in a coarse-precision speckle coordinate pattern database; wherein the coarse-precision speckle coordinate pattern is disposed in a coarse-precision speckle coordinate pattern database; wherein the coarse-precision speckle coordinate pattern database is created by following the steps of: specifying a measurement starting point on the target surface, capturing the coarse-precision speckle coordinate pattern with an invariant speckle pattern-capturing device as the first coarse-precision speckle coordinate pattern, specifying the first coarse-precision speckle coordinate pattern coordinate with a laser interferometer, moving the target by a coarse-precision speckle coordinate pattern displacement with a servo motor, capturing the coarse-precision speckle coordinate pattern with the invariant speckle pattern-capturing device as the second coarse-precision speckle coordinate pattern, recording the displacement of the laser interferometer to specify the second coarse-precision speckle coordinate pattern coordinate, and repeating the steps to finish creating all of the coarse-precision speckle coordinate pattern; wherein the coarse-precision speckle coordinate pattern database is created by capturing the positioning-oriented coarse-precision speckle coordinate pattern according to a rule below: 
 D≧ 2Δ,ε≧½ D,Δ+ε=D D: range of the capturing of the coarse-precision speckle coordinate pattern Δ: displacement of two adjacent coarse-precision speckle coordinate patterns ε: range of the overlapped capturing of two adjacent coarse-precision speckle coordinate patterns; wherein the fine-precision speckle coordinate pattern database is created by following the steps of: moving a target by a fine-precision displacement with the servo motor immediately after the first coarse-precision speckle coordinate pattern has been captured, capturing the first fine-precision speckle coordinate pattern with the invariant speckle pattern-capturing device, recording the first fine-precision speckle coordinate pattern coordinate specified by a laser interferometer according to a displacement, and repeating the above steps to capture the other fine-precision speckle coordinate patterns successively, capture P−1 fine-precision speckle coordinate patterns, and finalize the capturing of the first fine-precision speckle coordinate pattern relative to the first coarse-precision speckle coordinate pattern according to the positioning device positioning coordinate; and repeating step (A) to capture the other fine-precision speckle coordinate patterns and positioning coordinates successively.