This paper describes the effort of constructing the Olympic Oriented Trilingual Corpus for the development of NLP applications for Beijing 2008. Designed to support the real NLP applications instead of pure research purpose, this corpus is challenged by multilingual, multi domain and multi system requirements in its construction. The key issue, however, lies in the determination of the proper corpus scale in relation to the time and cost allowed. To solve this problem, this paper proposes to observe the better system performance in the sub-domain than in the whole corpus as the signal of least corpus needed. The hypothesis is that the multi-domain corpus should be sufficient to reveal the domain features at least. So far a Chinese English Japanese tri-lingual corpus totaling 2.4 million words has been accomplished as the first stage result, in which information on domains, locations and topics of the language materials has been annotated in XML.