Abstract: Elaborated in the paper are the chemical composition and design scheme of the X80Q steel tube used as the offshore platform leg support. The key process control points for manufacture of the tube are summarized，and the best heat treatment process is determined via relevant tests. Furthermore，the mechanical properties of and welding process for the tube are evaluated. The test results lead to such a conclusion that with low C and Mn-containing steel as the base material，and owing to addition of micro-alloy elements namely，Cr，Mo，Ni，V，Ti and Nb，the strength of the tube is enhanced，and its grains are refined to reduce its thermal sensitivity. With 930℃quench temperature and 625℃temper temperature，the tube possesses homogeneous microstructure and fine grains. Moreover，both the mechanical properties and welding performance of the tube are good，and satisfactory to the customer requirements.