Based on the characteristic of magnetic fluid whose viscosity can be manipulated by external magnetic field,a mechanical seal hydrodynamically lubricated by magnetic fluid was developed and the adaptive control method of sealing performance was proposed.The adaptive control system designed is mainly composed of parameter monitoring system,coarse adjustment system,microadjusting system and fluid replenishing system.The coarse adjustment system can shorten the response time of the adaptive system,while the microadjusting system can improve the precision of adjustment.The combination of them can ensure the stability of the sealing system.By comparing the pressure of lubrication film and the pressure of sealing medium,the control system can judge whether the sealing performance of the mechanical seal can meet the sealing requirement.If the rotational speed of rotating ring or the pressure of sealing medium are changed,the system will adjust the voltage of the magnetic field generator according to the preset strategy to change the viscosity of the magnetic fluid,so as to regulate the hydrodynamic pressure of the liquid film and adjust the input flow rate of the magnetic fluid.Then the sealing capability of the mechanical seal can be adjusted according to fluctuations of operating conditions in real time.The control program was tested with kerosene as base fluid.The test results show that the control program can accurately adjust the sealing performance of mechanical seals.