英語教育對於台灣是一個重要的教育議題，而近年來台灣英語教育成果不盡理想。影響英語教育成果的因素眾多中，英語師資供需維持動態均衡與否，則是影響英語教育成效的重要因素。從1997～2008年為止，台灣共培育出148,766名合格師資，其中擔任正式教職者只有80,979位，供需失衡非常嚴重。事實上，影響師資需求的因素錯綜複雜、息息相關、環環相扣、互為因果，形成一個複雜且動態的系統。本研究利用系統動態學探討台灣中等教育英語師資供需系統結構，提出中等教育英語師資供需系統質性模式，並利用量化模式模擬相關政策效果。研究結果顯示，2015年起，台灣現任中等教育英語教師將產生超額供給，到2038年最嚴重，將產生3,630位超額供給。在政策模擬方面，本研究模擬最熱門並廣受討論的降低班級人數，模擬2013年每班學生法定人數上限降至25人，可有效解決2015年以後之超額教師問題；而增加英語每週授課時數，只能短期解決問題，對於長期的教師超額問題幫助不大。最後，本文也提出了一些具體的政策建議。

English education plays a vital role in Taiwan. Unfortunately, it has achieved little success. The disequilibrium between supply and demand of English teachers has been found to be one of the major factors. Between 1997 and 2008, Taiwan certified 148,766 teachers; however, only 80,979 of them are currently holding official teaching positions, indicating a serious discrepancy between supply and demand. What affects the supply and demand balance is complicated; the factors are closely intertwined, and they are found to form a complex dynamic system. Grounded in the so-called system dynamics, the current study aims to investigate the structure of supply and demand of secondary English teachers in Taiwan and to provide a useful simulation model for making relevant educational policies. Our findings indicate that, starting the year of 2015, the supply of secondary English teachers in Taiwan will exceed the demand. The surplus will amount to 3,630 by the year of 2038. Our policy simulation model indicates that cutting class size to 25 students per class, which has been strongly recommended and widely discussed by scholars, starting in the year of 2013 is the most effective solution to the problem of disequilibrium between supply and demand of secondary English teachers in Taiwan. All the other solutions proposed by scholars, including increasing English class hours and raising the retiring age to 60, are not found to be as effective. Implications of the model are discussed in the final section of the paper.