Reducing low-melting impurity content in thermal barrier coatings (TBCs) can improve the high temperature stability and service life of coatings. But there is rare quantitative study on the relationship between the low-melting impurity content and coating properties. In the present work, the effect of SiO₂, Al₂O₃, and Fe₂O₃ impurities on the properties of Yttria-Stabilized Zirconia (YSZ) TBCs prepared by atmospheric plasma spraying was investigated. The samples were prepared with the contents of these impurities being increased gradually from less than 0.01wt% to 1.00wt%. The results demonstrated that those low-melting oxide impurities exhibit a significant effect on thermal conductivity and porosity of the coatings, playing a key role on thermal shock failure. The performance of coatings deteriorated especially significantly when the impurity oxide content is less than 0.2wt%.