Abstract: A sample irradiation electron source is developed to study the early earth environment and life evolution process. The electrons are emitted by the hot filament,the electron energy is determined by the cathode voltage,and the electron beam spot size is determined by an electrostatic lens. The filament winding method increases the uniformity of electron emission. According to theoretical analysis and electromagnetic software simulation,the parameters of the distance between the cathode and the control pole are determined. The simulation results show that when the energy is 3.5 keV,the larger the focusing voltage,the smaller the beam spot. When the working distance is 150 mm,the beam spot diameter can be adjusted from 30 to 50 mm. The experimental results show that the energy of the electron beam emitted by the device is continuously adjustable between 1 and 5 keV. When the working distance is 150 mm,the spot diameter of the 3.5 keV electron beam can be adjusted,which is consistent with the simulation results and can produce a 20.8 μA electron beam.