To study the thermal effect of composite configuration grazing-incidence slab amplifier, a composite configuration was used, in which the Sapphire with high thermal conductivity was bonded on the pump face of the laser medium Nd:YVO₄ crystal.The thermodynamic model of the grazing-incidence slab amplifier was built up. The temperature distribution, optical path difference and thermal lens effect were analyzed theoretically in detail. Also, the temperature distribution, thermal strain, optical path difference and thermal focal length were simulated by finite element analysis software COMSOL. The results indicate that compared with single medium structure, the maximum temperature of the composite configuration decreased by 60 K, and the maximum deformation of the pump face decreased by 1/3, while the pump power is 60 W, the thickness of the slab is 2 mm and the thickness of the bonding layer is 1mm. The novel composite configuration has reduced the thermal effect effectively.