We systematically investigate the influence of annealing effect on terahertz (THz) generation from CoFeB/heavy metal heterostructures driven by femtosecond laser pulses. The THz yield is achieved to increase triply in W/CoFeB through annealing effect, and doubly in Pt/CoFeB. The annealing effect originates from both the decrease of synthetic effect of THz absorption and the increase of hot electron mean free path induced by crystallization, with the latter being dominant, which is experimentally corroborated by THz transmission measurement of time-domain spectrum and four-probe resistivity t. Our observations not only deepen understand the spintronic THz radiation mechanism but also provide a novel platform for high speed spintronic opto-electronic devices.