Currently, brittle mechanics and designing methods of high-strength construction-structure steel and its weld at low temperature are little studied at home or abroad. In addition, global climatic anomalies bring with extremely low temperature at cold region from time to time in recent winters; therefore it is imminent to research about the rule of the brittle fracture of high-strength construction-structure steel at low temperature. The main mechanical properties of steel are precondition and foundation for its toughness studying. In this paper, uniaxial tensile test of Q460C(14mm at thick), the high-strength construction-structure steel has been carried out at the low temperature to obtaining the intensity index (including yield strength σs, tensile strength Rm), the plastic index (including elongation at break A, reduction of area Z), and the rule of these index along the temperature changing, as well as calculating the Q460C steel’s temperature sensitive coefficient, which may be used to forecast the intensity index of Q460C at low temperature. The experimental data show that: The yield ratio of the Q460C was found to increase with the elongation at break A and the reduction of area Z decreasing while the plasticity and toughness decrease as the testing temperature drops. The result indicates that the Q460C steel is inclined to low temperature brittle fracture, so brittle fracture prevention measures should be strengthened.