Material properties of permanent magnet in the magnetic fluid seal are important factors that determine the sealing effect. However, the relationship between the magnetic properties of permanent magnet and the failure-pressure has not been studied quantitatively in the available research. In this work, the relationship between material properties of permanent magnet and the failure-pressure of magnetic fluid seal was obtained from theoretical analysis and numerical simulation. The permanent magnet was changed in materials to calculate the failure-pressures of a typical magnetic fluid seal. The result shows that the failure-pressure of magnetic fluid seal grows with the maximum magnetic energy product of permanent magnet increases at the beginning, whereas there is a turning point. After that, the failure-pressure decreases as the maximum magnetic energy product increases.