The invention discloses a double-cooling oil chamber welded type integrally-steel-forged internal combustion engine piston and a fabricating method thereof. The piston comprises a piston upper par and a piston lower part, which are formed through welding; the ring-shaped cooling oil chambers, which are arranged in the middle in the piston head part at the lower part of a combustion chamber, and a basin-shaped cooling oil chamber, which is arranged along the interior of a ring groove, are communicated with each other through oil holes; an oil outlet connected with the basin-shaped cooling oil chamber is formed in the middle of the upper part of the piston lower part; the lower part of the oil outlet is connected with a piston inner chamber; the ring-shaped cooling oil chambers are connected with the piston inner chamber through oil inlets; the piston upper part and the piston lower part are separately forged; the cooling oil chambers are formed through welding after the piston upper part and the piston lower part are respectively processed, so as to simplify the process of forging a piston blank and that of forming the sealed oil chambers, and accordingly the structural strength of the piston is higher; and with the two cooling oil chambers, the working temperature of the piston can be reduced so as to improve the reliability.