Deep web is web database accessed by the web search, it is different from surface web, so technology of traditional search engines is not applied to deep web research very well. Some key technology of deep web search was researched, including automatic discovery of deep web resource and ontology-based information extraction of deep web. Effectiveness of these technologies and relevant algorithms were verified through experiments. Based on these technologies and relevant algorithms, a deep web search system was implemented, it could access deep web resource and extract structured data for various applications. The system has been applied to national important project "national portal of science and technology infrastructure" and has achieved obvious effect.