We have developed an information object system targeting at the preservation and sharing of long-life digital contents. An information object is an entity that encapsulates the required data and methods in a unit. In this paper we present the design of the system function to create a compound information object by composing some basic information objects. A compound information object is a portable and extensible unit that can serve for various kinds of applications in information services. We will present the mechanisms and the related issues in the composition of information objects.