The objective of this paper is to examine the structure of technology spillover from UAV(unmanned air vehicle) technology to other industries by applying patents analysis. The network analysis on patent data of USPTO(United Stated Patents and Trademark Office) from 1981 to 2000 was adopted to investigate the characteristic change of the technology spillover The results show that the influence of the UAV technology to other industries has grown over the twenty years period. For the weapon system development, this study provides a research basis to estimate the technology spillover effects on industries. Searching a structural niche from the inter-industrial knowledge flow structure might be a useful technique to find core technologies which generate large technology spillover on the other industries.