The invention discloses high-strength high-toughness low-temperature steel at 50 DEG C below zero and a manufacturing method thereof, and belongs to the manufacturing field of low alloy steel. The low-temperature steel comprises chemical compositions in percentage by weight: 0.12 to 0.20 percent of C, 0.15 to 0.50 percent of Si, 1.20 to 1.70 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, 0.30 to 1.00 percent of Ni, 0.005 to 0.050 percent of Ti, 0.005 to 0.10 percent of Al, 0.010 to 0.050 percent of Nb, one or more than one of less than or equal to 0.10 percent of V, less than or equal to 1.0 percent of Cu, less than or equal to 0.50 percent of Mo, less than or equal to 0.040 percent of Zr, and less than or equal to 0.20 percent of RE, and the balance being Fe. The manufacturing method for the steel comprises the following steps: the heating temperature of steel billets is between 1, 150 and 1, 280 DEG C, the heating rate is between 8 and 14 minute/centimeter, the initial rolling temperature of the steel is more than or equal to 1, 100 DEG C, the accumulated reduction rate of control rolling is more than or equal to 60 percent, the reduction rate of each of final three passes is more than or equal to 10 percent, and the final rolling temperature is between 780 and 860 DEG C; and the normalizing heat treatment is adopted, the keeping temperature of the normalization is between 850 and 930 DEG C, and the keeping time is 30-50 minutes+plate thickness (millimeters) x 1 minute/millimeter.