Abstract: Series of impact test was carried to a kind of 390 MPa grade high strength low alloy(HSLA) steel produced by thermo mechanical control process (TMCP) to study its low temperature toughness, and the correlation of low temperature toughness and microstructural characteristics was also investigated. The results show that the low temperature toughness of the steel was good. The impact absorbing energy was 127 J at -40 ℃ which was much higher than the specifications of related standard, and ductile-brittle transition temperature(DBTT) was -56 ℃. Cleavage crack propagation direction deflected frequently because of its fine effective grain size, which increased the resistance to the cleavage fracture, so the steel has excellent low temperature toughness.