This work is designed to research the quantitative relationship between the structural characteristics of atmospheric plasma spraying thermal barrier coatings (APS-TBCs) and the CMAS penetration rate in a high temperature environment. The influence of microcracks, holes, and other defects on the penetration behavior was analyzed. The ZrO2-8% Y2O3 (YSZ) coating was prepared by the atmospheric plasma spraying method. The surface of the coating was deposited by CMAS with the molar ratio of 45SiO2∶33CaO∶13AlO1.5∶9MgO. The CMAS penetration test was implemented at 1 200 ℃ with different exposed time. Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and x-ray powder diffractometer (XRD) were employed to analyse the microstructure and phase of the coating. The image method and processing software were used to analyse the porosity and pore size distribution of the coating. The penetration rate of CMAS related to coating structure was measured. The molten CMAS can penetrate the coating quickly, and the pores of the coating were filled to a large extent. The penetration depth of the CMAS increases with the penetration time increasing. In this case, CMAS penetrated about 200 μm within 30 s. The porosity of the coating decreased from 12.8% to 4% when the CMAS penetration time was 5 minutes. The porosity of the coating was 3.8%, when the CMAS penetration time was 10 minutes. The filling behavior of CMAS in the pores will not change with an increase over time. CMAS had good penetration behavior once pores with an equivalent diameter of less than 3 μm, and exhibited the opposite trend once pores equivalent diameter was greater than 3 μm. The effective porosity with an equivalent diameter of less than 3 μm introduced into the calculation of the CMAS penetration rate decreases the deviation between the calculated results and the measured results from 13% to less than 5%. The YSZ coating did not undergo significant phase change until 30 minutes after CMAS penetration began. The YSZ coating has a large number of micropores and the cracks were also observed when the CMAS penetration time sustained for 1 h. The area around the cracks in the coating was corroded soseverely that it accelerated crack propagation. The phase transition degree of YSZ coating and powdered coating degradation area increases with the increase of CMAS penetration time. The diameter of the microcracks included in the atmospheric plasma sprayed YSZ coating has significantly influenced the penetration rate of CMAS, but the degree of tortuosity has not. The cracks with smaller diameters accelerate penetration rates, but those with larger diameters have the opposite effect. Atmospheric plasma sprayed YSZ contains a large number of microcracks with small diameters that cause structure to be identified in a short period of time after CMAS penetration. In addition, long-term CMAS penetration will cause large-scale corrosion pits in the YSZ coating. It is also found that penetration of CMAS is a gradient decay process, and the corrosion degree decreases sequentially from the top to the bottom of the coating. The expansion of microcracks caused by CMAS corrosion can greatly promote the spalling failure of the coating.