Abstract: X70 pipeline steel was air-cooled or water-cooled at room temperature after heat treatment at 650-800℃, and the effects of heat treatment on the microstructure and properties of X70 were analyzed by OM and SEM. The results show that when the heat treatment temperature reaches 700℃, the microstructure is composed of ferrite and a small amount of MA islands. As the temperature increases, the content of MA islands in the microstructure increases, and the water cooling process retains a higher proportion of MA islands than air cooling process at room temperature. After heat treatment, the plasticity of X70 pipeline steel shows an upward trend, but the strength decreases gradually with the increase of heat treatment temperature. When the temperature exceeds 700℃, the yield strength can no longer meet the requirements of X70 steel grade.