Abstract: A method for manufacturing a retardation film by using a dual-axial stretching process uses a PMMA to produce a cast film. The cast film is stretched in both a proceeding direction and a width direction simultaneously by 1.0˜5.0 times in both the length and the width. By using a predetermined annealing temperature to co-coordinate shrinking of the film in both directions simultaneously, decrease of the refraction ability caused by the stretching can be controlled. To attain high uniformity of the optical characteristics of the film, the surface temperature of the film during the stretching process is controlled within a predetermined range, then the optical variation thereof is improved, and thus the following optical characteristics are achieved: R0: 0˜3 nm and Rth: ?40˜0 nm; wherein R0=?*?Te+?*?Xe+?*?Ts+?*?Xs+C1 and Rth=a*?Te+b*?Xe+c*?Ts+d*?Xs+C2.