Multipass deformation simulation tests were performed on a high strength low alloy (HSLA) steel by using a Gleeble3800 thermomechanical simulator to study the continuous cooling transformation behaviors and the resultant microstructures. Based on the transformation temperatures or transformed microstructure volume fractions，the models for phase transformation of the tested steel were constructed. The results showed that there were ferrite，pearlite，bainite and martensite transformation occurring in the high strength low alloy steel. And the validity of the models for phase transformation temperatures or microstructure volume fractions resulting from the experimental data was confirmed.