Gear shaft is one of the key components for transmitting torque and speed in automotive transmission. Deflections will inevitably occur after heat treatment. It is necessary to ensure the straightness of the parts by straightening. During straightening process, cracks often appear and result in scrapped parts. This paper focuses on the situation of high straightening crack rate of internal input shaft in one dual-clutch automotive transmission, makes an in-depth analyses the pressure straightening process theory, crack generation mechanism, working process and crack detection system. After studying on the case hardened gear shaft material properties, elastoplastic process theoretical basis, crack characteristic and finite element simulation, etc., This paper has systematically improved straightening crack performance and proposes three crack rate improvement methods by using finite element analysis to find out optimal punch point which can reduce the maximum stress value; increasing the punch increments and adopt vector straightening to improve the straightening procedure; reducing the gas quenching pressure in the heat treatment process to improve the mechanical properties of the parts, etc. Finally, the scrap rate of straightening crack was reduced from 1.95% to 0.14%.