The dielectric response of SBN:Ce ceramics to the 532 nm cw laser was investigated at room temperature by means of a terahertz time-domain spectroscopy. When the external laser field is imposed onto the SBN:Ce ceramics, the permittivity of the sample shows an appreciable change with amplitude variation up to 8.5% and the dielectric loss increase 15%, respectively. The refractive index |Δn| varies linearly with the intensity of the applied laser. The photo-ferroelectric physical mechanisms of SBN:Ce ceramics can be attributed to the internal space field in the ceramics caused by the light excited free carries with the analytic models. The results present important references for design and selection of the terahertz tunable devices.