The invention discloses a series-connected double-wire type combined 
welding wire for CO2 gas shield high-speed flat 
fillet weld. The series-connected double-wire type combined 
welding wire for the CO2 gas shield high-speed flat 
fillet weld comprises an antecedent 
electrode welding wire and a posterior 
electrode welding wire, the antecedent 
electrode welding wire and the posterior electrode welding wire are connected in series, the antecedent electrode welding wire is formed by a first steel-tape sheath and 
metal cored 
powder contained inside the first steel-tape sheath, the weight of the 
metal cored 
powder is 10-30% of the total weight of the antecedent electrode welding wire, the antecedent electrode welding wire is high in 
deposition rate, the quantity of generated 
slag is small in a 
welding process, and a small amount of added 
fluoride enables the 
electric arc to be more stable. The posterior electrode welding wire is formed by a second steel-tape sheath and welding flux 
powder contained inside the second steel-tape sheath, the weight of the welding flux powder is 10-30% of the total weight of the posterior electrode welding wire, the content of the diffusible 
hydrogen of deposited 
metal can be reduced to be lower than 5ml / 100g through the posterior electrode welding wire, and CO released by 
combustion of an undercoat can be reduced by Al and Mg in the 
welding process. A small amount of 
titanium and 
boron are added in both the metal cored powder and the welding flux powder, and the 
impact value of the deposited metal can be improved greatly. When welding is carried out at the welding speed higher than 1.5m / min, the combined welding wire is excellent in 
welding process, and good paint resistant performance can be obtained.