This paper proposes a method for encoding, macro-coding and utilizing design knowledge for computer aided conceptual design. From VE (Value Engineering) perspectives, we interpret artifacts as communication channels which transmit a designer's intention to the "world of structures" in which the designer's intention is substantiated. This transmission process is subjected to teleological, causal and information theoretic rationality. The information transmission is optimized by introducing intermediary "codes" (schema of design knowledge) which bypass the channel. By means of Explanation-Based Generalization and Genetic Algorithm, codes prepared in the initial knowledge-base are combined together into the so-called "macro-codes". Codes and macro-codes are evaluated by their efficiency of accelerating design process, by their rationality of using themselves, and by their fitness for design phase. We propose a computer environment for supporting conceptual design which retains several codes sorted out by three dimensions of evaluation, and facilitates designers to select their desired codes. In this environment, processes of conceptual design take the form of placing selected codes at appropriate locations along with the information transmission channel.