The invention provides a cement slurry with long-term-integrity cement sheath for a heavy-oil thermal-recovery well. The cement slurry comprises, by weight, 100 parts of thermally responsive cement, 25 to 65 parts of water and 0.2 to 8 parts of a cement slurry aid. The thermally responsive cement comprises 30 to 60 parts of oil well cement, 10 to 20 parts of active silicon powder, 0 to 10 parts of hollow glass beads and 10 to 50 parts of a thermally responsive composite material. The thermally responsive composite material comprises 20 to 30 parts of clay mineral, 10 to 20 parts of fly ash and/or vulcanic ash, 5 to 20 parts of rubber powder and/or latex powder, 3 to 10 parts of carbon fiber, 10 to 15 parts of nanometer silicon dioxide, 5 to 10 parts of calcined magnesia, 10 to 20 parts of ultrafine superfine slag powder and 5 to 10 parts of inorganic whiskers. The cement slurry provided by the invention can solidify at normal temperature; and set cement can resist long-term high temperature, and the mechanical properties and thermal properties of the set cement in a high temperature environment are integrally adaptive to strata and casing pipes.