Abstract: There are two methods to calculate the triode system of electron gun:First method is Continuous Emitting method, it regards the cathode emitting as a continuous action, so it can only calculate a few of electron trajectories, and takes short time. Because it calculates a continuous cathode emitting, the error of calculation is big. The second method is Monte Carlo method, it calculates the cathode emitting with random method, and then calculates many random electron trajectories. The error of this method is smaller than Continuous Emitting method, but it will take a lot of time. This paper discusses a new method, it regards the cathode emitting as a continuous action when the value of electric field is not very precise, then it uses Monte Carlo method to calculate triode system when the value of electric field is precise. This new method decreases the error of calculation and saves time of computation.

Key words: emitting system of electron gun, continuous emitting method, Monte Carlo method, electron emitting