In the future of aeroengine technology, silicon based ceramic matrix composite (CMC) has important applications as structural materials for the hotsection components, which, in the combustion environment, needs to be protected by multifunctional thermal and environmental barrier coating (TEBC). The threshold requirements for the design of advanced TEBC system include low thermal conductivity, which protects the CMC substrates from thermal attack; and compatible thermal expansions with substrates, in order to minimize the thermal stress during thermal cycling. Therefore, a comprehensive understanding of the coordinated mechanism of thermal conduction and thermal expansion for candidate materials, from the perspective of “material genome”, is a key challenge. In this paper, the structural characteristics, heterogeneity of interatomic bonding, phonon dispersions and phonon anharmonicity for rareearth disilicates (β-, γ- and δ-RE2Si2O7, RE=Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) are studied based on firstprinciples calculations combined with lattice dynamics. Intrinsic lattice thermal conductivity (κL) and coefficient of thermal expansion (CTE) are calculated, and the “gene” that controls the thermal properties of RE2Si2O7 polymorphs are discussed. It is found that lowfrequency optical phonons are obviously coupled with acoustic phonons, and the high anharmonicity for lowfrequency phonons is the origin of low κL for β, γ- and δ-RE2Si2O7. Besides, the “gene” that controls the thermal expansions of RE2Si2O7 polymorphs are found to be the linear or bent configuration of Si—O—Si “bridge”, which determines the positive or negative anharmonicity for lowfrequency phonons, as well as the bulk modulus, and finally lead to obviously lower CTE for β- and γ-RE2Si2O7 as compared with δ-RE2Si2O7. These results highlight that, the anharmonicity for low-frequency phonons, i.e. the “magnitude” and the “positive or negative” values, is the key for coordinated tuning of κL and CTE for RE2Si2O7. These understandings bring new inspirations for the design and optimization of TEBC systems.