The study analyzed individual income tax data from 31 provinces in China from 2001 to 2010 to understand its impact on income distribution. Provinces were grouped by income levels, and the pre-tax and after-tax Gini coefficients were compared. The research found that individual income tax has weakened its regulation on income distribution, especially in middle and low-income provinces. In recent years, this trend has become more pronounced. The effectiveness of income gap regulation through individual income tax varies among provinces, suggesting the need for tax system reform and tailored tax policies based on each province's circumstances to strengthen the positive impact of individual income tax on income inequality.