A 4-dimethylamino-N''-meth-yl-4''-stilbazolium tosylate (DAST) crystal grown by spontaneous nucleation method can realize a tunable broadband THz radiation source. Effects of mass concentration of saturated growth solution on the crystal growth morphology and optical quality are investigated, and the vibration and rotation characteristics of the chromophore are analyzed by the Raman spectrum of the crystal. Using the high-energy and tunable dual-wavelength laser within the wavelength range of 1.3--1.5 μm as a pump source, the broadband THz radiation output in the range of 0.1--20.0 THz is achieved by the 0-phase matching external-cavity different frequency and galvano-optical fast scanning technology. The maximum output energy of each pulse is 3.59 μJ at 18.9 THz, and the energy conversion efficiency is 2.39×10 -4. Based on the broadband THz output spectrum, it is found that the absorption of THz wave by the DAST crystal is mainly caused by lattice vibration.