For further optimizing the personal income tax rate in China, and making it more efficiently in adjusting income distribution and increasing its speed of international process, we provide the pattern of upended "U", the upper limit of optimized marginal tax rate and the range of paying taxes of levying the highest marginal tax rate of personal income tax according to the most suitable tax theory and the drawback of personal tax rate in China, the mathematical method. The personal income tax rate function of optimization is also given. We finally get the advancements of it in income distribution and international process through putting it into practice and comparing to the former rate.