Effect of pre-strain and aging temperature on mechanical property and microstructure of X70 pipeline steel was investigated by means of scanning electron microscope ( SEM ) and transmission electron microscope ( TEM ). The results indicate that the X70 steel shows a microstructure compopsed of granular bainite, acicular ferrite and M/A. The aging temperatures below 300℃, exhibit nearly no effect on the microstructure and the tensile strength of the steel. With the rising of aging temperature, the quantity of activated interstitial atoms, therewith, the pinning effect on dislocations increases, which leads to the gradual increase of the yield strength; However, when the temperature raises to above 200℃, the recovery of pinning effect occurs resulting in the decline of the yield strength. With the rising of aging temperature, the hardening of material induced by the increased cottrell atmosphere and precipitations leads to the decline of the impact toughness. With the increase of the pre-strain, the increment of dislocations may lead to the increase of yield strength, and the stress concentration will increase at boundries of the hard brittle phase M/A, therewith increase the probability of the formation micro-cracks, as a result, the impact toughness delines.