The invention relates to a replacement method of a converter slag trap, which comprises the following steps: moving a slag wagon provided with a trap bin to below the slag trap to be maintained, putting the demounted slag trap to be maintained into the trap bin by using a chain hoist, and taking away the slag wagon with the slag trap to be maintained; and moving a complete slag trap to the position near the demounted slag trap by using the slag wagon, hoisting the complete slag trap to the original position of the demounted slag trap by using the chain hoist, and fixing. The method has the advantages of low cost, high safety and high speed, and is capable of enhancing the replacement efficiency of the slag trap, shortening the replacement time and reducing the participation of the maintainers; the replacement of one slag trap can be accomplished by 6 persons for 6 hours; and the method can avoid aerial work, thereby ensuring the safety of the working personnel.