Over the last ten years, sulfuric acid dewpoint corrosion has become a more important concern in refinery furnaces since sulfur levels in fuels have increased. Electroless nickel phosphorous coating is one of the most widely used industrial coatings owing to its good corrosion resistance in many highly corrosive environments. In this work, electroless Ni-P-SiO2 composite coatings were prepared on AISI 1020 carbon steel. And the corrosion behaviors of Ni-P-SiO2, Ni-P coatings and carbon steel substrate were evaluated by immersion, electrochemical tests in 5%wt sulfuric acid solution, and dewpoint corrosion tests in simulated furnace flue gas. The experimental results indicated that corrosion resistance properties of Ni-P-SiO2 coating was best, followed by Ni-P coating and carbon steel was worst.