The invention provides an austenitic heat-resisting stainless steel welding electrode for ultra-supercritical thermal power units, comprising deposited metals, to be specific, 0.03-0.10% of C, 1.0-2.5% of Mn, </=0.80% of Si, 24.0-26.0% of Ni, 21.5-23.5% of Cr, 1.5-2.5% of Mo, 2.5-3.5% of Cu, 0.30-0.60% of Nb, 3.0-4.0% of W, 1.0-2.0% of Co, 0.15-0.30% of N and the balance of Fe and impurities. TheCaO-CaF2-SiO2 slag system formulation is used herein, trace alloy elements are added, the main deposited metals include 25% of Ni, 22% of Cr, 3% of Cu, 3% of W and 1% of Co, welding processibility isgood, deposited metal tensile strength Rm is >/=720 MPa, ductility is >/=35%, and normal-temperature KV2 is >/=50 J.