本文最主要探討稅捐規避防堵的法理論歸屬，亦即法律解釋以及漏洞填補。稅捐規避存在於被規避法條的可能字義的解釋範圍外，然而又被法條的目的所包含，因此它存在於漏洞之中。透過類推適用雖可填補，但是在稅法不利類推禁止的規範下，類推適用的法續造方式並無法有效的防堵稅捐規避。因此，德國稅捐通則第42條稅捐規避防堵的概括條款具有重要的地位。它透過特殊的法適用方式─「事實擬制」，亦即，藉由與經濟過程不相當的法律形成擬制成合乎經濟過程的事實，並賦予其應有之稅捐義務。在這樣的思維下，雖可與稅捐通則第42條的法適用理論─「外部理論」作為聯繫，然而與此相對的「內部理論」在事實擬制的過程中，亦扮演重要的角色。總結而言，德國稅捐通則第42條規定在稅捐規避防堵上具有獨特之地位，其法條構成要件以及特殊的漏洞填補方式實則融合了內部以及外部理論。此外，透過德國稅捐通則第42條之分析，亦重新檢視我國稅捐稽徵法新增訂之第12條之1有關實質課稅原則之適用。

This text mainly discusses the legal theory of tax circumvention, that is, the law interpretation and the loophole filling. Tax circumvention goes out on the possible meaning of a word of the provision which is avoided, however it is to be included the purpose of the provision, therefore, it is existed in the region of the loophole. Through the analogy it can be although filled up, but under a ban on the deepening analogy in the tax law the development of the law by analogy can not effectively defend tax circumvention. Therefore the General rule of Section 42 Fiscal Code of Germany plays an important role. It applies the way through the special method-＂the fact fiction＂, that is, the economic process, which is not equal with the law formation, should have to become the equal fact with the economic process, and give it the tax obligation. Under the thinking like this, although it can connect the external theory, which is one of the theories of the application of the law by the General rule of Section 42, however it is also about the teleological interpretation of the law, therefore it agrees with the contents of the internal theory. In a word, the special method of the loophole filling by Section 42 connects in fact the internal and external theory. In addition, through the analysis of Section 42 Fiscal Code of Germany, also re-examine the new order about Substance over form Principle, which added in 2013 in the Fiscal Code of Taiwan.