This paper presents a systematic approach to interior engine sound design for enhancing sound character of car interior sound effectively. Nowadays an active noise control technology is widely used in vehicle industry. Particularly, an active sound design (ASD) technique using vehicle's audio system for controlling interior sound due to powertrain has become a general method to improve sound quality or character. The ASD system using speakers has the advantage of creating various sounds relatively easy. In this study, the novel systematic approach is proposed to guide the efficient design of powerful and pleasant acceleration sound by order spectrum analysis. At first, primary attributes of powerful and pleasant sound were analyzed and sound concept was derived. Secondly, the optimal linearity and the level envelope of firing order were derived by subjective evaluation. Next, the engine orders arrangement was analyzed under the aspects of musical harmonic theory on six cylinders engine. The level ratio of harmonious orders for pleasant sound was also evaluated. And the novel powerful index based on booming and rumbling was developed and used for determining powerful sound target set-up. Finally, powerful and pleasant acceleration sound for six cylinders engine were suggested. These sounds have been implemented through the ASD.