An improved 09CrCuSb steel resistant to sulfuric acid dew point corrosion. The chemical composition of the steel is, by mass percentage, 0.04-0.12% of C, 0.20-0.50% of Si, 0.35-0.90% of Mn, lower than or equal to 0.030% of P, lower than or equal to 0.030% of S, 0.70-1.10% of Cr, 0.25-0.60% of Ni, 0.25-0.50% of Cu, the content ratio of Ni to Cu being greater than or equal to 1, 0.04-0.10% of Sb, lower than or equal to 0.02% of Ti, 0.02-0.04% of Alt, greater than or equal to 0.0005% of Ca, lower than or equal to 0.007% of N and the balance of Fe and impurity elements. The products are in the forms of hot-rolled steel plates and hot-rolled round tube blanks. For the steel plates, the yield strength is greater than or equal to 345 MPa, the tensile strength is greater than or equal to 490 MPa, the ductility is greater than or equal to 25%, the Charpy impact energy is greater than 100 J at -40 °C, the sulfuric acid dew point corrosion resistance is at the same level as that of the traditional 09CrCuSb, and the plate thickness can reach 40 mm. The sulfuric acid dew point corrosion resistance of the round tube blanks prepared according to such composition likewise is at the same level as that of the traditional 09CrCuSb.