The invention discloses a precise forming method for a cylindrical straight gear and a device thereof, and aims to solve the problem of inconsistent equipment and technology in the prior art. The method comprises the following steps of: 1) determining the cylindrical blank (2) of a gear, and baiting according to the size; 2) installing and debugging a die on an adjustable hydraulic press which is in double acting on the top and the bottom; 3) according to the material of the cylindrical blank (2), determining and heating the cylindrical blank (2) to a determined temperature value; 4) primarily forming the heated cylindrical blank (2) into a long tooth-shaped tooth blank (9); 5) precisely forming the primarily formed long tooth-shaped tooth blank (9) into a standard involute cylindrical straight gear; 6) conveying the standard involute cylindrical straight gear which is formed by precise forming into a thermoplastic precise forming nitrogen protection anti-oxidation system, and cooling to the normal temperature; 7) sawing a formed big-thickness involute cylindrical straight gear into a plurality of cylindrical straight gear with the set thickness or single formed small and medium thickness involute cylindrical straight gear by a band saw, and entering a machining working procedure.