Z玻色子衰变到tau轻子对的tau极化测量，是验证标准模型，检验轻子普适性的重要途径，而计划建设的CEPC作为高统计量的Z玻色子工厂，可实现对tau极化的精确测量。本研究基于CEPC末态粒子重建算法框架PFA，对重建出的末态粒子进行信号事例的选择重建，然后对筛选的信号事例的运动学参量分布进行统计，采用最大似然法获得tau的极化测量结果。本项目的研究重点是进一步提高tau极化测量的精度。同时对与其相关的物理量弱混合角进行计算，对精确验证标准模型提供有价值的参考。

The measurements of the τ lepton polarization in Z boson decay is an important way to test the SM and the hypothesis of the universality of leptons. As a factory of Z boson, the tau polarization can be measured accurately at The Circular Electron Positron Collider(CEPC). In this project, based on the final particle reconstruction framework PFA, the signal events can be reconstructed and selected from the final particle objects. Then the τ polarization can be measured by using a maximum likelihood method on the distributions of kinematic variables . The sources of systematic errors are the key factors which impact on the quantitative of the τ polarization measurements, so they will be studied emphatically to improve the precision of the τ polarization measurements. The weak mixing angle will also be calculated in this project, which will be useful to the precision test on the hypothesis in the SM.