In this paper, the effects of deformation temperature, strain rate and deformation on the hot deformation behavior and microstructure of as-extruded ZA21 magnesium alloy were investigated. The processing map was established, and the immersion weight loss and electrochemical tests were carried out on the unstable zone, the safe zone and the best processing zone to study the corrosion behavior in different regions of ZA21 magnesium alloy. The results show that the dynamic softening mechanism of ZA21 magnesium alloy is mainly dynamic recovery at high temperature and low strain rate, and dynamic recrystallization is dominant at low temperature and high strain rate; The optimum processing temperature is 300~350 °C, and the strain rate is 0.001~0.01s-1, which is mainly related to the generation of complete dynamic recrystallization; Under the same processing technology, with the increase of deformation, the self-corrosion potential of ZA21 magnesium alloy is obviously positively shifted, and the self-corrosion current density is significantly decreased. When the amount of deformation increases to 60%, the self-corrosion current density can be reduced by 3~4 orders of magnitude. This is mainly because the grain refinement leads to a denser oxide film on the surface of the alloy; However , the microstructure of the processing instability zone has wedge cracks and obvious pores, so the corrosion rate is relatively large.