Abstract: Studied in the paper are the effects by different heat treatment processes on the microstructure and mechanical properties of the X70QS linepipe for service under low-temperature and acidic conditions.As a result, the facts as below are revealed.The quenching process produces obvious effect on the structural properties of the said linepipe, i.e., along with the rising of the quenching temperature, the bainite structure is remarkably coarsened, and thus the mechanical properties, particularly the low-temperature impact property are obviously reduced.Moreover given the quenching temperature reminds unchanged, reducing the quench-cooling speed will get the ferrite structure gradually increased, and polygonized, which significantly leads to poor strength.Thanks to being(water)quenched at 880~900℃ and tempered at+600℃, the X70QS linepipe for service under low-temperature and acidic conditions obtains the best strength-low-temperature toughness matching.