When the rolling temperature was 350℃, the angular velocity of the roller was about 3.14rad/s and the wall thickness reduction rate was 20%, 30% and 40% respectively, the coupled thermo-mechanical numerical simulation of the AZ31B magnesium alloy tube with the size of 50mmX7mmX1000mm in continual mandrel rolling process was carried. Then, the research on the damage stress and the distribution of temperature field of the simulation was conducted on the condition that the magnesium alloy tube was at the same rolling temperature but differ in reduction rate.The results show that: when the rolling temperature is same, the maximum damage value of the AZ31B magnesium alloy tube and the heat generated by the plastic deformation is increased with the increase of the wall thickness reduction ratio. With the location of the maximum damage value appears in the roller gap. And, because of the large heat exchange between the roller and the tube, the temperature of the roller gap is higher than the top of the roller, and the temperature difference is increased with the increase of the Wall thickness reduction ratio.So, when in the same rolling condition, the damage of magnesium alloy tube in Longitudinal rolling is smaller than the magnesium alloy sheet.