A metal substrate for flue gas-denitration catalyst that, like SUS304, can be used without corroding is provided by improving the corrosion resistance of SUS430 substrate that is inexpensive and can easily be supplied stably. A method for producing the metal substrate for flue gas-denitration catalyst, wherein the method comprising the steps of: lath-processing a band-shaped steel plate made of ferrite stainless steel into a band-shaped metal lath; (1) degreasing process oil adhering to the metal lath; (2) passing the metal lath through a solution containing phosphoric acid and surfactant to load the solution; (3) draining off the excess solution; and (4) drying and heating the solution-loaded metal lath to react the phosphoric acid with the substrate, in which respective steps are carried out sequentially to form a film of phosphate compound on a surface of the substrate.