Smoothing by spectral dispersion (SSD) technology has been widely used for many high-power laser drivers. However, due to the engineering design reasons, national ignition facility (NIF) and technical integration experiment line (TIL) use only one grating. It will affect the smoothing efficiency, especially at the beginning time. But we can reduce it by the way of optimizing the modulation frequency. Finally we analyse the SSD technology with one grating and provide a theoretical basis for the optimization of high-power laser drivers.