為解決不動產交易分別就土地及房屋課徵土地增值稅及財產交易所得稅、公告現值及評定現值與房地市價之落差、公告現值調整之僵固性及房地售價比例不當安排等因素而產生違反租稅公平及量能原則之情事，我國自民國105年1月1日起施行房地合一課稅制度；惟於所得稅法及所得基本稅額條例之稅制整合後，個人若利用私法自治契約自由原則，將實質之不動產交易轉化為形式上之證券交易，因該交易標的物為證券而非不動產，故是類交易非屬房地合一稅課徵範圍。為防杜此一濫用私法自治契約自由原則而產生之租稅規避問題，短期而言，先由揭穿公司面紗原則，就如何防杜濫用公司法人格予以探討；再由實質課稅原則之運用，說明如何防杜稅捐規避。長期而言，為符合法律保留原則，並維持租稅安定性，仍應經由增（修）訂法律之程序，憑以規定人民納稅義務方為法治國家之根本。 In a real estate transaction, the house and the land associated were subject to Property Transaction Income Taxes and Land Value Increment Taxes. However, the summation of land’s Assessed Present Value and the house’s appraisal value is quite different to the real estate market value. Other critical issues in real estate transaction taxation include the adjustment of the Assessed Present Value is inflexible, and the assignment of the value proportion between the land and house could be purposely arranged in an inappropriate way. These difficulties may cause concerns in fairness and Ability to Pay principal in taxation. To counter these issues, the administration adopted the Consolidated Housing and Land Taxation since January 1, 2016.Nevertheless,after the integration of the Income Tax Act and the Basic Income Tax Act, individuals may exercise the autonomous principle of private law that could change a real estate transaction into a form of a security exchange. In this sense, the transaction objective is a security rather than a property. This transaction would not fall into the scope of Consolidated Housing and Land Taxes.To prevent tax-avoidance via the abuse of free-to-contract principle in autonomous Private law, firstly, this study recommends that the administration should adopt the piercing the corporate veil principal. It may reveal the ways to prevent the abuse legal entity status. Secondly, the administration should use the Principle of Substantive Taxation. This principle could prevent tax avoidance. In the long term, the administration should comply to principle of legal reservation and maintain taxation stability. The adoption of these principles can be achieved through the amendment / approval of related laws, to delineate citizens’ taxation obligation as a legal foundation of a constitutional nation.