Abstract: According to the motion characteristic of the charge in the electric and magnetic fields, the principle for measuring electron charge mass ratio using electron magnetic focusing is analyzed. The method for measuring field current with magnetic focusing is discussed from the theoretical point of view by using principle of magnetic fields superposition, and vaious methods are compared. The experimental data are analyzed and managed from the experiment point of view, the one of the main reason of error production is pointed out and the new method for measuring the value of field current with magnetic focusing is obtained.

Key words: electron charge mass ratio, field current, environmental magnetic field, magnetic focusing, elecric focusing, error