The invention discloses a preparation method of an upper tool post of a cold-rolled flying shear. The method comprises the following steps: step 1, establishing a relative parameter equation, which conforms to a mechanical principle, according to parameters; step 2, by taking a highest point K of a lower shear blade as a beginning computing point, according to design requirements, giving an equidistant division length on the direction of a shear blade width L, and analyzing conditions of a half of the shear blade width; sep 3, solving a space track of a point U of an upper shear blade and a point K of the lower shear blade; step 4, searching an angle interval; step 5, solving a shear blade backlash compensation value of the upper tool post, which is relative to the point K of the lower shear blade; and step 6, solving a shear blade backlash compensation value of the upper tool post, which is relative to the point M(i) of each section of a lower shear blade section. According to the preparation method provided by the invention, through a space equation analysis method, requirements of a cold rolling process is combined, motion characteristics of the upper shear blade and the lower shear blade of the flying shear are analyzed, and the shear blade backlash of the cold-rolled flying shear is solved by using a circulating iterative value method, thereby achieving design of the cold-rolled flying shear more clearly.