In the investigation, the microstructural observation and quasistatic tension experiments of X80 pipeline steel were conducted so as to reveal the effects of the cooling rate on its quenched dual-phase microstructure formation and strain-hardening behavior. The results show that (1) a dual-phase microstructure including ferrite and bainite is obtained after X80 pipeline steel is quenched; (2) the ferrite volume fraction and the uniform elongation increase with the decrease of the cooling rate while the strength decreases; (3) when the ferrite volume fraction is not less than 5.27%, the strain-hardening exponent has a positive correlation with the uniform elongation but a negative correlation with the yield ratio; (4) when the ferrite volume fraction reaches up to 22.8%, the work-hardening rate decreases with a fast stage and then a slow stage, and the latter stagethe later stage delays the necking point; and (5) with the decrease of the cooling rate, the lath-like bainite in the quenched microstructure turns to be granular and MA phase forms, simultaneously, the strain-hardening performance of the quenched microstructure is guaranteed and the uniform plastic deformation ability is improved by means of the conversion of the dislocation strengthening to the second phase strengthening.