The invention discloses non-quenched and tempered steel and a method for manufacturing an automobile semi-axle by using the non-quenched and tempered steel. The non-quenched and tempered steel is prepared from the components in percentage by mass: 0.43-0.47% of C, 0.50-0.80% of Si, 1.20-1.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.035% of S, 0.15-0.30% of Cr, 0.10-0.15%of V, 0.01-0.05% of Al, less than or equal to 0.045% of Nb, 0.015-0.035% of Ti, 0.01-0.02% of N, less than or equal to 0.25% of Ni, less than or equal to 0.10% of Mo, less than or equal to 0.03% of Sn, less than or equal to 0.20% of Cu and the balance of Fe and impurities. According to the non-quenched and tempered steel and the method for manufacturing the automobile semi-axle by using the non-quenched and tempered steel, the high-performance micro-alloyed non-quenched and tempered steel is adopted to replace 42CrMoH quenched and tempered steel for the implementation of a semi-axle controlled-forging and controlled cooling manufacturing process, and the quenching and tempering heat treatment process is eliminated, so that energy consumption of the automobile semi-axle manufacturing can besaved by 40-50%, the cost can be reduced by 10-20%, meanwhile, deformation and cracking caused by quenching during quenching and tempering can be reduced, the straightening process is simplified, andthe technical level reaches the domestic leading position.