The invention discloses a method for mixed burning of natural gas and calcium carbide furnace gas, which uses a filter, a front pressure-relieving valve, a rear pressure-relieving valve, an on-site controller, a remote control system, a combustion furnace, a molten salt furnace, an air preheater, a final concentrator and a molten salt tank, which are connected in turn. By researching and developing a method for mixed burning of natural gas and calcium carbide furnace gas in a process step for producing caustic soda in pearl by evaporating solution of sodium hydroxide, the problem of comprehensive utilization of furnace gas generated in a closed calcium carbide furnace is solved, the calcium carbide furnace gas resource is effectively used, natural gas resource is saved, and the pollution of calcium carbide furnace gas to the environment is avoided effectively. The method can be widely used in a production process using natural gas as fuel, particularly a process step for producing solid caustic soda by evaporating the solution of sodium hydroxide.