1. A method for generating over-drive values applied to a 3D display device used with shutter glasses, the 3D display device comprising a first gray scale of a pixel for displaying a first-eye image and a second gray scale of a corresponding pixel for displaying a second-eye image, the method comprising the steps of: measuring a plurality of brightness values shown by using a plurality of first-eye gray scales in every n scales and a plurality of second-eye gray scales in every n scales at a first-eye channel of the shutter glasses; linearly interpolating the brightness values into N×N brightness values which consist of N first-eye gray scales respectively corresponding to N second-eye gray scales, wherein n and N are positive integers and N>n; calculating N×N crosstalk values of the N first-eye gray scales respectively switching to the N second-eye gray scales according to the N×N brightness values, wherein the N×N crosstalk values comprise a plurality of rising crosstalk values and falling crosstalk values; and determining a first over-drive gray scale and a second over-drive gray scale according to the N×N crosstalk values, such that the brightness value of the pixel being in the second over-drive gray scale and the corresponding pixel being in the first over-drive gray scale is about equal to the brightness value of both the pixel and the corresponding pixel being in the first gray scale and such that the brightness value of the pixel being in the first over-drive gray scale and the corresponding pixel being in the second over-drive gray scale is about equal to the brightness value of both the pixel and the corresponding pixel being in the second gray scale.