Abstract: The producing mechanism of secondary electrons in sealed neutron generator is discussed and several methods to suppress secondary electrons are introduced. The PIC simulation is carried out for the different methods. The result indicates that only a part of secondary electrons can be suppressed by Faraday cylinder and a part of them can enter into the accelerating gap to form electron current. The secondary electron current is about 1/5 of emitting current of secondary electrons on target. But almost all secondary electrons can be suppressed by electrostatic field combined with Faraday cylinder and the secondary electron current is about zero when the deflection voltage is 300 V.