Abstract: Based on the tensile test of 63 steel specimens at different temperatures from 20 ℃ to －165 ℃，mechanical properties and changing trend of three types steel bars ( HRB335，HRB400 and cryogenic reinforcements) were analyzed. The results showed that the yield strength fy，the ultimate strength fu of the steel bars increased whereas the percentage elongation after fracture 5，percentage reduction of area decreased with the temperature decreasing，which means the reducing plasticity of steel bars. The influence of temperature on elastic modulus was little and the elastic modulus fluctuated around a certain value. The shape of the stress-strain curve changed little at different temperatures，however，the cooling environment led to the reducing plasticity and improving brittleness， reflected in the dropping ultimate strain.