Abstract: The main problem in the application of nano-ferrofluid sealing magnetic field is how to find a way to estimate the sealing capability. There are many factors affecting the sealing capability, for example, the characteristics of nano-ferrofluid, the structure of magnetic pole, the process of load function, etc., in which the structure design of magnetic pole is the most important factor for the sealing capability of magnetic field. The numerical analysis method was used to simulate the distribution of magnetic field of the sealing device and experimental investigation was made to study the influence of the structure parameters of a typical magnetic pole on the sealing capability. These experiments indicated that numerical simulation and regression equation calculation could reflect the sealing capability. By considering a specific tolerance the regression equations could be used as the guidance in designing nano-ferrofluid sealing device.