Abstract: Usually, the design optimization only deals with individual component of the truck because of the complex coupling relation between the cab and frame of the truck under assembly environment. Focusing on the complete optimal problem, a new conception of static modal stiffness was introduced and the sensitivity of static modal stiffness was defined. The method for computing static modal stiffness sensitivities was also developed. Above proposed method has been applied to analyze and design the truck's cab, where a finite element model for full vehicle was used and the cab was divided into 15 super-elements. It is concluded that the obtained static modal stiffness sensitivities could be used to improve the design of the cab.