Abstract: In this paper, a kind of micro-focus cold cathode X-ray tube with a very high electron passing rate is established by using Computer Simulation Technology Particle Studio software. The effect of X-ray tube structure on focal point, electron passing rate, and cathode emission current is studied emphatically. In particular, following the structure of the Pierce electron gun, a curved is adopted, and a cathode groove is added on this basis, so that the electron passing rate is increased from 75.21% to 90.26%, while the focus of nearly 500 μm is reduced to less than 50 μm. Under the condition that the anode voltage is 90 kV and the gate voltage is 1000 V, the electron pass rate of the cold cathode electron gun can reach 95.41%, and the effective focus size at the anode target surface is about 45 μm.