This paper studies the industrial structure and degree of industrial diversification of Taoyuan County since 1986 to examine if Taoyuan Aerotroplis will meet one of the successful key factors of industrial diversification. It begins with a discussion of strategic analysis on critical factors of Taoyuan International Airport and finds out one of the important factors of successful aerotroplis lies in industrial diversification. This research is conducted by adopting quantitative approach and applying coefficient of industry diversity to value the degree. The Location Quotients (LQs) ratios are applied as well, providing a way to examine the specialization of economic activity in Taoyuan County. The finding reveals that the industrial structure of Taoyuan County is secondary industry from 1986 to 1991. After 1991, the tertiary industry grows enormously and now it trends to service-oriented market. Also, industrial diversification of Taoyuan County is toward positive and high degree of diversity in industry since 1986. Taoyuan County has a relatively higher concentration of employment in manufacturing than Taiwan since 1986. Health Care Services industry, Water Supply and Remediation Services industry and Transportation, Storage and Communication industry are industries which increase concentration of employment in Taoyuan County. This research suggests that the authority concerned could make use of the positive condition of diversity in industry to accelerate industrial cluster in development of aerotroplis that strengthen the competitiveness of Taoyuan Airport and attract more cargo and passengers traffic. Further research is suggested by enlarging the areas such as Taipei County development axis or Hsinchu County, by broadening the sample of the industry scope and classification systems to subsectors, industry group or industry and by comparing the industrial diversification of Taoyuan Aerotroplis with that of the other countries which succeeds in aerotroplis models.