The dynamic viscosity of fluid is an important parameter to describe the viscosity movement of fluid There are many methods to measure the fluid dynamic viscosity in experiment, such as rotating cylinder method,falling ball method,capillary method and so on.In this paper,based on the simple pendulum movement of a common magnetic ball,using the Hall element measuring magnetic field in different time, and the location of the different time is obtained by analysis of variation of the magnetic field,the location of the magnetic ball is obtained by fitting oscillation amplitude over time,finally the value of the dynamic viscosity of air will be obtained through data analysis.