Abstract: Investigated are the effects by different quenching and tempering processes on the microstructure and mechanical properties of the Q390E steel pipe for offshore engineering by means of mechanical property testing and microstructure analysis.The results indicate that after being quenched at 890℃ and tempered at 690℃, the microstructure of the Q390E pipe is completely bainite, and has the best strength-low temperature toughness matching;and that the actual A_c1 temperature of the pipe is about 690~710℃, and at the same quenching temperature, when the tempering temperature is going up to 710℃, and the pipe is tempered at a two-phase zone, and proeutectoid ferrite obviously developed in the matrix microstructure, which leads to seriously deteriorated lowtemperature impact toughness, increased tensile strength, and decreased yield ratio of the material.