The application of thermal barrier coatings (TBCs) as an effective passive heat protection measure for turbine blades is widely employed. However, applying thermal barrier coatings can lead to aerodynamic changes in the blade passage and film cooling holes. Three-dimensional numerical simulations are conducted for a specific type of engine turbine guide vanes through uniform application of TBCs. The study focuses on the effects of two parameters, namely, TBC thickness and surface roughness, on the characteristics of film cooling holes, guide vane passage flow, and film cooling effectiveness. The results indicate that the application of TBCs leads to a decrease in film hole mass flow coefficient, an increase in total pressure loss coefficient and energy loss coefficient in the guide vane passage. Additionally, the aerodynamic losses in the guide vane passage and film holes are positively correlated with TBC thickness. However, the application of TBCs effectively enhances the cooling effectiveness at the base of the blade. As the TBC thickness increases, the cooling effectiveness at the base of the blade improves. Furthermore, the temperature reduction rate increases with the increasing TBC thickness. When the ceramic layer thickness reaches 0.4 mm, the average cooling effectiveness at the base of the blade increases by 19.1%, with a temperature reduction rate as high as 6.5%. Due to the low thermal conductivity of TBCs, the surface cooling effectiveness decreases with the increasing TBC thickness. When the surface roughness of TBCs changes, it is observed that as the surface roughness increases, the film hole mass flow coefficient decreases, and the total pressure loss coefficient and energy loss coefficient in the guide vane passage increase. Moreover, both the cooling effectiveness at the base of the blade and the average surface cooling effectiveness decrease with the increasing surface roughness. When the surface roughness height of the coating reaches 20 μm, the decrease in cooling effectiveness at the base of the blade and surface cooling effectiveness is 7.2% and 8.9%, respectively. However, the temperature reduction rate increases with the increasing surface roughness, reaching 2.58% at a roughness height of 20 μm. In conclusion, within the parameter range studied in this work for TBC thickness and surface roughness, the addition of TBCs is beneficial for thermal protection on the blade surface. The cooling effectiveness at the blade surface increases with the increasing TBC thickness, but the rate of increase diminishes as the TBC thickness increases. Meanwhile, the thermal insulation effect of TBCs is enhanced, leading to an increasing temperature reduction rate with the increasing TBC thickness. However, increasing TBC thickness results in the increased flow losses in the guide vane passage and film holes. The aerodynamic losses in the film holes and guide vane passage increase with the increasing surface roughness, deteriorating the thermal protection effect of TBCs. Both the cooling effectiveness at the base of the blade and the surface cooling effectiveness decrease with the increasing surface roughness, while the thermal insulation effect of TBCs is strengthened. The temperature reduction rate is positively correlated with the surface roughness, increasing with the increasing surface roughness.