雖然1997年司法院大法官作成釋字第420號解釋，首次肯認「實質課稅原則」，但直至2009年5月13日立法院才終於增定稅捐稽徵法12條之一，將實質課稅原則納入法規，解決以往在租稅法律主義下缺乏法源根據的困境，使稽徵人員在民眾所採取的交易形式外觀上雖然不符合租稅構成要件，但實際上只要與常規交易下具有相同經濟實質時，能直接針對經濟實質予以課稅。 本研究利用我國五區國稅局十年統計資料，加入政策虛擬變數、時間趨勢變數以及其交互項進行迴歸分析，根據最小平方法(OLS)及固定最小平方虛擬變數模型(LSDV)，探討實質課稅原則入法後，因為稽徵執行力的提升，以平均罰鍰衡量納稅義務人租稅遵從度是否受到改變。 結果顯示實質課稅原則變數對於罰款變動有顯著正向效果，即增訂稅捐稽徵法12條之一更符合租稅法律主義，有助於稅捐單位稽徵效力的提升，所以可以顯著增加罰款收入；此外，本研究也發現實質課稅虛擬變數和時間趨勢交互項顯著為負，表示納稅義務人隨時間增加逐漸意識到稅捐稽徵法12條之一的重要性，故會減少規避行為使平均罰款額下降，顯示政府政策的執行會受到時間影響而產生不同效果。 / The concept of The Principle of Substantive Taxation got approval from No. 420 constitutional interpretation by the Grand Justices in 1997 for the first time, but not until May 13, 2009 did the legislature promulgated 12-1 of the Tax Collection Act in article. Take the Principle of Substantive Taxation into legislation, tax collector have more convincing reasons to solve the dilemma of “Principle of Taxation under the Law”. Most important, it emphasizes the beneficiaries of economic substance as taxpayers, instead of according to the surface of tax regulations to determine the taxpayers. This study use panel data from National Tax Administration of five regions to examine the effects of the legislature promulgated 12-1 of the Tax Collection Act in 2009. We adopt the methods of ordinary least squares (OLS) and Least Square Dummy Variable Model (LSDV), and adding the reform dummy variables, time trend variable and its interaction term into regression to examine whether the enhancement of tax enforcement could increase the average fines or not. The results show that the reform dummy variable has a positive and significant impact on tax evasion collections per fine, that is formulated 12-1 of the Tax Collection Act more in line with the Principle of Taxation under the Law. Besides, the interaction term of reform dummy variable and time trend variable has a negative effect on per fine, which means that taxpayers gradually realize the importance of the regulation over time after the reform. Therefore, taxpayers will reduce tax evasion behavior to decrease the fine collections.