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.