Thermal and environmental barrier coating (TEBC), the up-to-date concept, is introduced to protect silicon-based ceramics matrix composites (CMC) from not only high temperature water vapor but also the alkali salt from volcanic ash and dust suspending in atmosphere. Because both of high temperature steam and CMAS will make Si-based CMC deteriorate rapidly. By executing the corrosion test against high temperature water vapor, we find that Si/Y2SiO5 double-layer TEBC can effectively protect SiCf/SiC CMC from water vapor at 1300 ℃ for over 205 hours. Almost all Y2SiO5 transform into Y4.67(SiO4)3O after corrosion test. It is also found that in CMAS corrosion test, the reaction zone formed between CMAS and Y2SiO5 layer prevents the mutual diffusion of elements in CMAS and Y2SiO5 layer. The apparent activation energy of reaction between CMAS and Y2SiO5 in 1200~1300℃ temperature ranges is calculated to be 713.749kJ/mol. These findings provide a reference to select appropriate materials for TEBC.