The work aims to study the erosion-corrosion behavior of pipeline steel X70 at different velocity in high- temperature and high-pressure CO2 saturated environment. The change trend of wall shear stress under different jet velocity was obtained by computational fluid dynamic (CFD) method, and a jet impingement simulating flow loop was used to study the influence of jet velocity on the CO2 erosion-corrosion of pipeline steel X70 through scanning electron microscopy (SEM), surface morphology profile apparatus, Vickers micro-hardness tester and metal loss measurement. The wall shear stress and compressive stress of the sample increased gradually as the jet velocity Uexit increased. With the increase of the distance to the jet center (radial distance), the wall shear stress increased firstly and then decreased and the wall compressive stress rapidly decreased. At a low velocity (Uexit≤10 m/s), the characteristic impingement angle was approximately 23° at the maximum wall shear stress location, but the characteristic impingement angle increased rapidly to 45° and then changed mildly at high velocity (Uexit≥20 m/s). The macroscopic morphology of samples showed obvious three regions:stagnation region, transition region and wall jet region, and the region distribution was more obvious at low velocity. At a jet velocity of 20 m/s, the wall shear stress presented the axial symmetry shape of “M” based on the sample center, and the erosion contour (depth of erosion-corrosion) of the sample surface presented a symmetrical shape of “W”. The maximum depth of erosion-corrosion was about 55 μm and appeared near the maximum wall shear stress, about 4 mm far from the stagnation region of sample center. The surface hardness of sample decreased with the increase of radial distance, and the hardness in the central stagnation region was up to 340HV10. When the jet velocity increased from 10 m/s to 40 m/s, the erosion-corrosion rate increased from 11.856 mm/a to 32.969 mm/a. The typical morphology of X70 pipeline steel is related with value of wall shear stress and influence of CO2 corrosion, and the erosion-corrosion is most serious at the location of maximum wall shear stress. The erosion-corrosion rate is regarded to be directly proportional linear to the velocity, Rcorr=4.861+0.714×Uexit.