Abstract: The principle and the current application fields of the magnetic fluid seal technique are introducedin this paper.Both the main advantages and disadvantages of the magnetic fluid seal technique in each application field are described by comparison with conventional mechanical sealing.The structure,the operation mechanism and the request on magnetic fluid of the magnetic fluid sealing device are analyzed.It is pointed out that the magnetic fluid with high saturation magnetizability and the sealing device with high intensity ofmagnetic filed are the two key factors.It is considered that the design optimization,limit breakthrough andexploitation of wider application can enable the magnetic fluid seal technique to develop further.