本論文主要研究在電源產品中共模電感的阻抗優化。共模電感的阻抗是對於電磁雜訊中EMI抑制的重要參數，在不同頻率有不同的阻抗值。本研究使用權重滿足幾個特定頻率中達到最高的阻抗，並使用田口方法中望大特性找出阻抗的最佳化。透過兩次田口實驗，第一次田口實驗考量7因子與14個交互因子並使用L32 (2^31)找出阻抗高的方向並縮小改善範圍，實驗結果顯示鐵芯尺寸，繞線圈數與鐵芯廠商是三個最主要的影響因子。第二次田口實驗則是以不斷改進的概念，在固定第一次實驗的5個因子並作針對2因子(線徑與圈數)再進行參數優化找出最大的阻抗。 依據最佳化實驗結果，優化後的結構其阻抗特性較原本提升了64.5%，在不須額外投入製程設備與成本下，大幅提高了產品的特性。且實驗找出的關鍵因子也減少了工程師試誤的次數與費用，提高公司的獲利。 ;This research focuses on impedance improvement in common mode choke used in power supply. The impedance is the key parameter to inhibit the EMI (Electro Magnetic Interference) noise while it varies through frequency. In order to find the best setup by using Taguchi method LTB (larger the better), we used weights to enlarge some particular frequency bandwidth to make the highest impedance in this research. We did two-stage Taguchi experiments. For the first stage, we considered 7 factors and 14 Interaction factors by using L32 (2^31). The result showed that core size, winding turns, and core vendors are the three most important factors that affect impedance performance. For continuous improvement, we fixed 5 factors from the first stage and did experiment with 2 factors (wire turns and wire diameter) to find the optimal setup in the second stage. The improvement structure has 64.5% better performance than the original one in impedance. Moreover, without investing in additional manufacturing equipment and costs, the EMI inhibit characteristics of the product had highly improved. The key, the impedance, found by this experiment reduced the costs of trial-and-error by engineers and thus increased the profits of the company.