This paper reals with the structure and function of duel mass flywheel. Damping effects of engine rotational fluctuation are compared with those of pre-damper clutch and duel mass flywheel and driven- system behavior is estimated engine idle r.p.m. The reason of gear rattle noise is higher in summer than winter and driving longer period than initial driving is due to affection by drag torque changing. The above-contents can be used on the design of clutch system and transmission matching including engine and duel mass flywheel.