While being an essential business in banking industry and its important role in banks getting more and more prominent with the coming of E-commerce era, the computerization of bank's international trade financing is considerably difficult. The difficulty comes from the complicated operation process, the variety, and dynamic requirement of flexibility of the business, which make it almost a mini-banking system itself. The appropriate and sophisticated software method and technology are needed to build a computer system of this kind. This paper presents a methodology based on semi-finished component model, and addresses a technique to design and implement the system. The technique is featured by building system on a standardized data bus interface, a system framework with menu/icon GUI for general controlling, and clusters of basic object components for elementary business. The basic object components can be grouped, wrapped, assembled into main frame and customized to produce a runnable system for a specific application or adapted to business changing. It also provides a flexible interface for integration with general banking systems and a sound foundation for distributed network banking systems.