我国经济增长已经进入了降速提质的关键时刻，与此同时社会主要矛盾转化为人民日益增长的美好生活需要和不平衡不充分的发展之间的矛盾。收入不平等是导致新时代主要矛盾的重要原因，而收入分配机制设计的首要难题是：如何在兼顾效率与公平的原则下，健全“初次分配”与“再分配”调节机制，从而在经济发展的基础上谋求社会主要矛盾的有效解决。这正是税负归宿与最优税收理论针对的问题。本课题以商品税、所得税和资本税构成的税收组合为研究对象，对内生工资不平等下的税负归宿与最优税收体系展开基础理论研究。研究试图回答以下问题：（1）我国收入分布的特征及其变化规律是什么？（2）各税种在初次分配与再分配中的角色分别是什么，如何相互配合？（3）初次分配与再分配间有何互动机制？（4）什么可观测的统计量可用以表达上述最优税收组合？（5）我国生产技术、产业结构和收入分布的变化对税负归宿有何影响，对税制改革有何要求？

China's economic growth has entered a critical moment of speed reduction and quality improvement. At the same time, the main social contradictions have been transformed into the contradictions between the people's growing needs for a better life and unbalanced and inadequate development. Income inequality is an important cause of major contradictions in the new era. At present, the primary problem of income distribution is how to improve the adjustment mechanism of "primary distribution" and "redistribution" under the principle of both efficiency and fairness, so as to seek effective solutions to the major social contradictions on the basis of economic development. This is the problem of tax burden and optimal tax theory. This paper takes the combination of commodity tax, income tax and capital tax as the research object, and studies the basic theory of the tax burden and the optimal tax system under the endogenous wage inequality. The research attempts to answer the following questions: (I) what are the characteristics of China's income distribution and its changing laws? (II) what are the roles of various taxes in the initial distribution and redistribution, and how to cooperate with each other? (III) what is the interaction mechanism between initial distribution and redistribution? (IV) what observable statistics can be used to express the optimal tax mix described above? (V) How does the change of production technology, industrial structure and income distribution affect the tax burden and what are the requirements for tax reform?