The invention discloses a gas-shielded type welding wire for PH13-8Mo stainless steel. The gas-shielded type welding wire is composed of an outer skin and a flux core. The outer skin is made of a low-carbon steel strip, so that the defect of work hardening caused by an existing stainless steel outer skin in the wiredrawing process is overcome fundamentally. The components of the flux core approach the components of a parent material through proportioning, so that when the gas-shielded type welding wire is used for welding of the PH13-8Mo martensite aging stainless steel, spatters are few, the weld shape is attractive, and good welding manufacturability is achieved. The invention further provides a preparation method of the gas-shielded type welding wire. Fluorite, quartz, sodium carbonate and magnesium oxide are added into a binder and mixed, then sintering is conducted, and sieving is conducted after grinding; the sieved materials are mixed with metallic molybdenum, metallic nickel, metallic chrome, electrolyzed aluminium, iron powder, rutile, zircon sand, silicon iron, boron powder and rare earth, then drying is conducted, and thus the flux core is obtained; and the flux core is added to a U-shaped groove formed by rolling of the carbon steel strip, the U-shaped groove with the flux core is rolling-closed, drawn, straightened, coiled into a disc and packed in a sealed mode, and thus the gas-shielded type welding wire can be obtained. The preparation method is simple and easy to implement.