Environmental barrier coatings (EBCs) enable SiC_f/SiC ceramic matrix composites (CMC) to operate under high-temperature combustion conditions. They reduce the oxidation rate of SiC_f/SiC, the volatilization of the composites due to reaction with water vapor, and the surface temperature of the composites. Rare-earth monosilicates (RE₂SiO₅), owing to their excellent high-temperature durability, low thermal conductivity, and good phase stability, are used as the top layer of EBCs. However, they exhibit a high coefficient of thermal expansion (CTE), leading to thermal mismatch and inducing tensile residual stress (with a magnitude of several hundred MPa) in the coating, resulting in the formation of vertical cracks, which act as extremely-high-diffusivity paths for oxidation species transportation and silica volatilization. Therefore, regulating the CTE of RE₂SiO₅ EBCs and minimizing the CTE mismatch among constituent RE₂SiO₅ layers with SiC_f/SiC CMCs are critical for multilayered EBCs. Through atmospheric plasma spraying, a typical Yb₂SiO₅/Yb₂Si₂O₇/Si coating system and a tri-layer structured multicomponent (Y_1/4Ho_1/4Er_1/4Yb_1/4)₂SiO₅/Yb₂Si₂O₇/Si coating system with better matched CTEs were manufactured. Both the coatings remained adhered to the substrate during deposition and after annealing, and no mud cracks that would compromise the coating gas-tightness quality and delamination cracks were observed at any of the coating interfaces. In thermal cycling tests, (Y_1/4Ho_1/4Er_1/4Yb_1/4)₂SiO₅/Yb₂Si₂O₇/Si coatings showed a lifetime that is three times longer than that of conventional Yb₂SiO₅/Yb₂Si₂O₇/Si coatings. The failure mechanisms in thermal cycling were investigated via the finite element simulation of stress. It was found that the stress in the substrate was low, and the residual thermal stress was mainly concentrated on the top, inter, and bond layers and increased with an increase in temperature. Compared with that of the (Y_1/4Ho_1/4Er_1/4Yb_1/4)₂SiO₅ top coat, the Yb₂SiO₅ top coat showed obviously higher residual tensile stress, which contributed to a higher tendency for mud-crack formation and higher energy release rate, substantially reducing the coating's thermal cycling lifetime. Through neutron powder diffraction and pair distribution function (PDF) analysis, the average and local structures of RE₂SiO₅ were studied. Overall, the average and local structures did not differ significantly, both of which can be described using the C2/c structure. Nevertheless, the PDF results demonstrated some differences in the disorder degree of Si—O and RE—O coordination environments. In particular, Rietveld refinement results of the PDF showed lower local distortion degree of [ORE₄] tetrahedrons when compared with that of the average structure. It is effective to reduce the distortion degree of [ORE₄] tetrahedrons by introducing Y³⁺, Ho³⁺, and Er³⁺ into the Yb³⁺ sites of Yb₂SiO₅, and smaller distortion degrees lead to lower CTE values. Coordinative local disturbances introduced by strategic high-entropy design have been proposed as the key method for CTE regulation.