A rigorous development of Trustworthy Computing System (TCS) is an active research area in TROMLAB research group since TCS concept was initiated in 2002 by Microsoft Corporation. In TROMLAB research group a component-based development of TCS was initiated in 2005. Several tracks of research activities, including formal specification of components and component-based systems, formal assessment of trustworthiness properties, and a framework construction for developing trustworthy systems are in different stages of development, and completion. It is in this context this thesis has evolved. It contributes a Visual Modeling Tool (VMT), the front-end to the development framework, in which the developer can construct visual models of system components without being burdened by complex formalisms. The thesis identifies the functional and performance requirements of the VMT tool from the goal of TCS research in TROMLAB, provides a detailed design which itself is based on component technology, and illustrates with two case studies, CoCoME and Mine Drainage, the modeling steps and its user-centric features.