The work aims to select appropriate flow velocity for oil and gas transmission, and reduce harm of flow velocity to corrosion of pipeline steel. With L360 steel as experimental steel and flow velocity as variable, corrosion behavior of the L360 steel in H2S/CO2 acidic environment containing Cl- was investigated with autoclave, corrosion electrochemical behavior of the L360 steel was studied based upon polarization curves and AC impedance, microstructure, structural characteristics and corrosion product constituents of the sample were analyzed with SEM and EDS. Corrosion rate of the L360 steel was determined in weight-loss method. Provided experiment conditions were identical, corrosion rate at flow velocity of 5 m/s (0.4824 mm/a) was higher than that at 0 m/s (0.3696 mm/a). In electrochemical tests, experimental conditions corresponding to 3 states were identical, the corrosion degree of steel ranged from 0 m/s to 5 m/s at the flow velocity of 3 m/s. As the flow velocity increased, the corrosion product film was increasingly fractured on the surface of the sample. The main corrosion product was FeS. At the flow velocity of 0 m/s, a small amount of FeCO3 and FeC3 was generated, and at the flow velocity of 3 m/s, tetragonal iron and greigite were generated. As the flow velocity increased from 0 m/s to 5 m/s, the corrosion potential shifted negatively and corrosion current density increased. At the flow velocity of 5 m/s, the corrosion potential was the most negative, self-corrosion current density was the maximum, radius of capacitive reactance arc was the minimum, and the steel was most susceptible to corrosion. According to corrosion weight loss experiment and electrochemical experiment, as flow rate ranges within 0~5 m/s, the lower the flow velocity is, the less corrosive effect on L360 pipeline steel will be. In order to ensure safe use of pipeline steel and improve its service life, low flow velocity should be selected as far as possible provided that normal transmission of oil and gas is not affected.