本研究為利用田口法對高階自由曲面投影系統之光學設計與優化，並提出一種光學系統可將虛像投影至六公尺處且適用於直立窗戶（例如：汽車側窗、大樓玻璃窗、捷運車窗等）之設計。研究結果顯示，經由田口法之優化，光斑尺寸縮小4.3%，光斑標準差縮小26.6%；畸變量縮小7.2%，畸變量標準差縮小16.8%。利用田口法可大幅減少實驗次數與複雜運算達到提升成像品質之效果。;The study is the use of Taguchi methods to optimize the optical design of the high-order freeform projection system. We proposed an optical system which can project a virtual image to six meters. Also, the system is suitable for upright windows, such as vehicles, buildings, and MRT. The result of the study shows that through the optimization of Taguchi methods, the optical spots size is reduced by 4.3%; optical spots size standard deviation is reduced by 26.6%; and the distortion is reduced by 7.2%; the distortion standard deviation is reduced by 16.8%. Using Taguchi methods can greatly decrease the number of experiment times and complex calculations to achieve the purpose of promoting the quality of imaging.