The effect of compression on the rnicrostructures and flow behavior of WE43 magnesium alloy was investigated in this article.The relationship between flow stress and strain rate was discussed.According to the empirical formula ε = Aσn exp(-Q/RT),the value of heat activation of WFA3 magnesium alloys is 297.15 kJ/mol.A mechanism of deformation softening of WEA3 alloy in testing hot deformation was identified to be dynamic recrystallization.