Abstract: By decomposing the K index of taxation elements, this paper makes a vertical comparison on the equality effect of wage income tax between before and after the reform and a horizontal comparison between different taxation elements. The empirical result shows that China's wage income tax (WIT) has a weak stimulation effect on the social equity as a whole, but the tax reform in 2011 was harmful to it. As for the taxation elements, the tax rate and the tax exemption volume are in favor of income equality, while the social security deduction (SSD) has the reverse effect. Under different income levels, the reverse adjustment degree of SSD decreases with the increasing income of the taxpayers. Meanwhile, the different items of SSD have different reverse adjustment levels on the residents' income distribution, in which the housing accumulation fund (HAF) has the most obvious reverse adjustment effect. Therefore, it is suggested that in the future more attention should be paid to the equality effect of WIT so as to give full play to its role in fair income distribution; the tax exemption volume of WIT should be determined rationally so as to improve its progressivity; the SSD system should be improved, and a tax-transfer payment system should be designed in an overall manner.

Key words: wage income tax (WIT), equality effect, taxation element, social security deduction (SSD)