Abstract: Since reform and opening, evolution of tax system and innovation of tax collection have deviated from tax collection economic principle more and more seriously and the dislocation between theory and practice is prominent. After explaining logical relationship between "simplicity and complexity" in tax law, through theoretical connection between simple tax law and tax collection economic principle, and reviewing practice both at home and abroad, the idea that the essence of tax collection economic principle is structural simple tax law was proposed, and a new theoretical system of "four beams and eight pillars" was constructed. On the one hand, the growth of tax system complexity helps to promote tax law simplification into a development trend; on the other hand, if tax system design and collection innovation can be in line with a series of simplification goals, it will simplify excessive complicated tax system, consolidate effectiveness of simplified tax system, and reduce efficiency loss caused by tax system complexity. Under the guidance of structural simplicity tax law theory, tax system simplification tool types are more abundant, and simplification indicators are more scientific, which helps to enhance explanatory and normative power about tax law principle. Related reflection on and revision of entity and procedure tax system in a new round of fiscal and taxation system reform can make a new theoretical path to help deepen tax reform achievements.