In this paper, the effect of Al and Ti on the high temperature plasticity of Q390 microalloyed steel was studied. The high temperature tensile tests of two Q390 steels with different contents of aluminum and titanium (0.02%Al-0.01%Ti and 0%Al-0.02%Ti) were carried out on Gleeble 3800 thermal simulation test machine. The high temperature plasticity of the two steels was compared and analyzed by calculation of shrinkage ratio, fracture morphology and energy spectrum of the precipitates. The study indicated: The toughness of 0%Al-0.02%Ti steel is 12%-35% higher than that of 0.02%al-0.01%Ti steel in the III brittleness temperature zone. Aluminum has a negative effect on the high temperature plasticity of microalloyed steel, while titanium has a positive effect on the high temperature plasticity of microalloyed steel. Therefore, the surface quality of Q390 microalloyed steel is improved when Q390 is adopted the composition of 0%Al-0.02%Ti steel.