The hot deformation behavior of Q690 low carbon microalloyed steel was studied with compression tests on a Gleeble-3 800 simulator in the temperature range from 850 ℃ to 1150 ℃ and true strain rate from 0.01 s-1 to 30 s-1 . Based on dynamic materials model (DMM), the processing map for the Q690 steel was obtained, and the microstructure characteristics were studied with optical microscope. The results have shown that, when the true strain is less than 0.7, there are two efficiency dissipative peak regions (1 000~1 120 ℃, 0.01~0.37s-1 and 1 100~1 150 ℃, 3.16~30 s-1) and three processing instability regions(850~900 ℃, 0.01~0.32s-1 and 850~900 ℃, 10~30s-1 and 1 000~1 085 ℃, 1~30s-1) in the processing maps. The true strain is more than 0.8, there are two efficiency dissipative peak regions (1 025~1 100℃, 0.01~0.38 s-1 and 1 100~1 150 ℃, 3~30 s-1) , and the flow instability regions appear at the temperature of 850~900 ℃ and the strain of 0.01~30 s-1, as well as at the temperature of 850~1 100 ℃ and the strain rate of 1~30 s-1. The microstructures of the two peak efficiency regions are uniform, fully dynamic recrystallization grain, so the optimum processing parameters of hot deformation have been achieved.