The present paper established a mathematical model, according to the structure of the end-window transmission micro X-ray tube anode. And we discussed the relationship between the average thickness of electron beam targeting and the high voltage. Also we obtained the spectral intensity distribution characteristics of the emitted X-ray on the angle, meanwhile by the use of Monte Carlo, the authors simulated the intensity distribution characteristics of the spectrum in the direction of 2π. The results show that the average thickness of the micro X-ray tube anode target is about 2 μm, and we can get much better single-energy spectrum in the vertical direction of the incident electron beam within a few degrees. These conclusions have some theoretical significance for the structural design of the micro X-ray tube and the emitted spectrum monochrome applications.