It introduces an experiment of measuring charge-mass ratio of electron by the method of magnetron controlling. It was focus on analyzing the way of processing the experimental data. In addition, it presents the “Midpoint” method of dealing with experiment data systematically, combining the way of the “Half Saturation Current” and the “Intersection”. The charge-mass ratio of electron was about 1.65×10¹¹ C/kg and 1.81×10¹¹ C/kg with relative errors of 6.25% and 2.84% by using the method of half saturation current and intersection method, respectively. However, the charge-mass ratio of electron was about 1.74×10¹¹ C/kg with relative errors of 1.14% by using the method of “midpoint”. It can be found that the method of “midpoint” can obtain charge-mass ratio of electron with higher precision compared with the method of “Half Saturation Current” and “Intersection”.