High quality 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) crystals were grown by seed crystal method through adjusting cooling rate. The influence of cooling rate on crystal quality, optical properties and terahertz(THz) output characteristics of DAST crystals were explored. Additionally, the structure and purity of raw materials were characterized by applying nuclear magnetic resonance analysis method. X-ray diffraction rocking curve measurement of (001) plane of the as-grown crystals was measured by X-ray diffractometer. A best full-width at half-maximum (FWHM) narrowed as 57.6″ was obtained at the cooling rate of 0.1 ℃/d. Optical transmittance of the crystals grown under these conditions is 65% in the wavelength range of 780 nm to 1 576 nm. Moreover, using the differential frequency method wideband tunable terahertz waves in the range of 0.1 THz to 20 THz were generated from DAST crystals. At 18.8 THz, the maximum output energy of the terahertz wave is 0.477 μJ/pulse, and the corresponding energy conversion efficiency is 5.31×10-5.