With the development of automobile industry, the higher NVH performance is required for customers, and with drastically reduction of engine noise, the gear rattle noise generated by the impact between neutral gears inside transmission can be much easily perceived. It is well known that the torsional mode of powertrain system has a direct relationship with transmission gear rattle noise, the higher torsional vibration leads to more serious gear rattle noise. This paper establishes a torsional model of a front wheel drive automotive drivetrain, including clutch system, transmission box and equivalent load of a full vehicle in AMESim software. The experimental engine speed fluctuations at different gears are used to excite the torsional model. The influences of several parameters, including flywheel inertia, clutch stiffness, clutch hysteresis and drive shaft stiffness, on the 2nd order (major engine firing order for a 4-cylinder-4-stroke engine) torsional resonant frequency and the 2nd order torsional resonant peak of the transmission input shaft are analyzed by changing them alternatively. The model is validated by a comparison between the simulated and measured 2nd torsional resonant peaks. It is concluded that the optimized drivetrain parameters reduce the 2nd order torsional resonant peak of transmission input shaft effectively. Some control strategies are successfully applied to a prototype vehicle to reduce the gear rattle noise which meets the subjective evaluation criterion.