The invention discloses a manufacturing process for a metal expansion joint used for an exhaust system of a combustion gas turbine. Chromated nickel molybdenum alloy structure steel is selected as a blank. A chromated nickel molybdenum alloy comprises, by weight, 0.28-0.38% of carbon, 0-0.35% of silicon, 0-0.90% of manganese, 0.80-1.50% of chromium, 3.00-4.00% of nickel, 0.40-0.60% of molybdenum, 0-0.015% of phosphorus, 0-0.015% of sulfur, 0-2.0% of hydrogen, 0.10-0.20% of vanadium, 0-0.025% of titanium, 0-0.20% of copper, 0-0.05% of aluminum, 0-0.50% of residual elements, and the balance Fe. A tetraethyl orthosilicate inorganic high-temperature-resistant coating is selected for carrying out coating. The manufacturing process for the metal expansion joint used for the exhaust system of the combustion gas turbine can greatly improve the abrasion resistance, the compressive resistance, the high-temperature resistance and the corrosion resistance of the metal expansion joint, and improve the production efficiency of the metal expansion joint, and is convenient to operate.