Recent research progress of terahertz (THz) radiation generation based on the ultrafast spin dynamics is reviewed. The transient spin-charge conversion based on the inverse spin Hall effect and the Rashba-Edelstein effect is introduced, and it is pointed out that the ferromagnetic/non-magnetic heterostructure has been used to design a low-cost and high-efficiency THz radiation source. The efficiency and bandwidth of a spintronics-based THz emitter can be improved by optimizing layer thickness, growth conditions, substrates, and construction. The applications of the THz emission spectrum are outlined in the study of the ultrafast formation dynamics of the spin Seebeck effect.