While designing a composite pavement with an asphalt concrete (AC) overlaid on a concrete pavement slab, realistic estimation of the temperature distribution in the concrete pavement slab is crucial. The overlaid AC layer is expected to reduce the uniform temperature and temperature gradient in the concrete pavement slab, resulting in a reduction in its thermal deformation and stress. The effect of pavement temperature of the AC overlay on the uniform temperature variation and temperature gradient in a concrete pavement slab was investigated through numerical modeling. A numerical prediction of the temperature distribution in an AC-concrete composite pavement using a one-dimensional finite difference method (1D FDM) was established and validated using field measurement data. The effects of the AC overlay thicknesses and different climatic conditions on the uniform temperature variation and temperature gradient in the underlying concrete slab were investigated using the proposed numerical model, the results of which showed that the predicted temperature of the AC-concrete composite pavement were in good agreement with the field measurement data. The AC overlay considerably reduced the uniform temperature variation and temperature gradient in the underlying concrete slab. The degree of temperature reduction in the concrete slab was significantly influenced by the AC overlay thickness; however, it was slightly affected by climatic conditions.