A tensile test was carried out for the extruded AZ31magnesium alloy along extrusion direction at 200

4

00℃and strain rate from 10

-4

to 10

-2

s

-1

and the strain hardening rate-stress curves were plotted.The dislocation model of the third stage strain hardening and the relationship of the hardening parameter K

1

and the softening parameter K

2

in the model between the deforming temperature and strain rate were investigated.The results reveal that K

1

is decreased with increasing in temperature and decreasing in strain rate

namely the hardening rate decrease.At 200

3

50℃

the softening rate K

2

is increased

showing the increase of recovery.However

with temperature increased from 350to 400℃

K

2

keeps almost constant

which is related to that dislocation annihilation rate has reached a stable state at 350℃because all of the slip systems of the magnesium alloy are in operation at the temperature.