The invention relates to steel for a vanadium/niobium-contained motor train unit axle and a heat treatment process thereof. The steel comprises the following components in percentage by weight: 0.24-0.30% of C, 0.20-0.40% of Si, 0.70-1.00% of Mn, 0.90-1.20% of Cr, 0.70-1.30% of Ni, 0.20-0.30% of Mo, 0.10-0.60% of Cu, 0.01-0.04% of Zr, 0.03-0.06% of V, 0.015-0.040% of Nb, 0.001-0.005% of Ca, P not more than 0.010%, S not more than 0.008%, 0.0040-0.0060% of [N], T[O] not more than 0.0015%, 0.0015-0.045% of Als, and the balance of Fe and inevitable impurities; the structure of the steel is tempered sorbite and a little lower bainite, wherein the content of the tempered sorbite near the surface of the axle is 100%; the content of the tempered sorbite in 1/2 radius place of the axle is 80-90%; and the steel is obviously better than commercial steel in plasticity and toughness after heat treatment, is prominently higher than the commercial steel in fatigue limit, is excellent in strength and toughness matching, and is excellent in fatigue resistance.