When the working temperature of magnetic liquid is higher than the vaporization temperature,it will not only damage the surface active substances of magnetic liquid,but also cause the vaporization of magnetic liquid.In order to investigate the temperature characteristics of the magnetic liquid in the magnetic fluid seal,the relationship between rotational speed,shaft diameter and temperature of magnetic fluid rotary seal was studied based on the method of numerical calculation and experimental verification,and the transformation process of the magnetic liquid was analyzed when the working temperature is higher than the vaporization temperature of magnetic liquid.The results show that the maximum temperature of the magnetic liquid rotary seal appears at the contact position with the shaft surface,and the minimum temperature appears at the contact position with the bottom of the pole tooth.The maximum temperature of magnetic fluid increases with the increase of rotational speed and axial diameter.When the product of shaft diameter and rotational speed is equal in two working conditions,the temperature rise of magnetic liquid is the same.When the temperature of the magnetic liquid is higher than its vaporization temperature,the transformation occurs first in the magnetic liquid connected with the outside and near the shaft surface,and the transformation area diffuses inward in a parabola shape.At the same working temperature,the transformation volume fraction of the magnetic liquid decreases with the increase of the shaft diameter.