Provided is an E309L stainless steel lengthened welding electrode capable of being used for large-current welding. A coating contains marble, fluorite, rutile, dehydrated potassium feldspar, dehydrated mica, bismuth oxide, chrome green, magnetite, sodium carbonate, micro-carbon ferro chrome, electrolytic manganese metal, zircon sand, potassium fluoroaluminate, rare earth fluoride, chromium metal and metallic nickel, blending and even stirring are conducted according to the ratio of the coating, 15-20% of sodapotash water glass is added and evenly stirred according to the total weight of the coating, the coating and an ER308L welding wire are put in an oil pressure type welding electrode extrusion press to produce and prepare the lengthened welding electrode, and no coating cracks or flushing can happen when the large current is 170-180 A and the welding core length is 450 mm; though an ER308L welding core is adopted, the cladding metal chemical components meet the requirement of E309L chemical components through the coating transition alloy method, and therefore the welding electrode has good welding process performance and is stable in electric arc, convenient to operate, good in weld appearance during welding, and sediments are easily separated.