The effects of temperature and strain rate on the thermal deformation-behavior of Cu-P weathering steel were studied by using thermal simulator. And the true stress-true strain curves at different thermal deformation conditions were got. Then the features of the microstructure of the steel under different temperatures and strain rates were analyzed. The results show that with the same deformation dimensions and strain rates, when the deformation temperatures were higher, the recrystallization would proceed much easier, and the size of the recrystal grains could be also larger. And with the same deformation dimensions and temperatures, when the strain rates were lower, the recrystallization could also occur easier, and the proportion and size of the recrystal grains were larger.