In the process of conceptual design of large and complex engineering systems such as a nuclear power reactor, there must be various human works by several fields of engineers on each stage of design, analysis and evaluation. In this study, we have rearranged the design information to reduce the human workloads and have studied an efficient method to support the conceptual design works by new information technologies. For this purpose, we have developed two design support environments for conceptual design of a space power reactor as a concrete design target. When constructing an integrated design support environment, VINDS, which employs virtual reality (VR) technology, we focused on visualization of physical structure, functional organization and analysis calculation with full usage of easy perception and direct manipulation of VR. On the other hand, when constructing another asynchronous and distributed design support environment, WINDS, which employs WWW technology, we improved the support functions for cooperative design works among various fields of experts. In this paper, the basic concepts, configurations and functions of the design support environments are first described, then the future improvement is surveyed by their intercomparison.