1. A method for reducing crosstalk of a liquid crystal display, comprising: receiving digital information of an original left eye image and an original right eye image; determining if gray level values of pixels in each scanning lines of the left eye image is the same with that of a corresponding pixel in the right eye image; a first adjusting step for adjusting the gray level values of the pixels to be a first target gray level value of a first gray level table when the comparing result is the same; a second adjusting step for adjusting the gray level values of the pixels to be a second target gray level value combination of a second gray level table when the comparing result is not the same; transmitting the digital information of the left eye image and the right eye image after the first and second adjusting steps are executed for the pixels in all of the scanning lines; each of the gray level values of the first gray level table corresponds to one first target gray level values, each of the gray levels values of the second gray level table corresponds to one second target gray level value combinations, and the second target gray level value combination comprises the second target gray level value for the left eye image and the second target gray level value for the right eye image; and wherein the first gray level table and the second gray level table satisfy the relationships below: a maximum brightness is obtained from a brightness of the left eye image after overlapping the left eye image and the right eye image when the gray level value combination for the left eye image and the right eye image is 255/0; a minimum brightness is obtained from a brightness of the left eye image after overlapping the left eye image and the right eye image when the gray level value combination for the left eye image and the right eye image is 0/255, and the maximum brightness corresponds to the gray level value equal to 255; the minimum brightness corresponds to the gray level value equal to 0 so as to form a three dimensional gray level gamma curve; and a difference between the brightness of the second target gray level value of the second gray level table of the pixel after overlapping the left eye image and the right eye image and the brightness of the corresponding pixel on the three dimensional gray level gamma curve is within three percent; and a difference between the brightness of the first target gray level value of the first gray level table of the pixel after overlapping the left eye image and the right eye image and the brightness of the corresponding pixel on the three dimensional gray level gamma curve is within three percent.