Abstract: The primary spectrum of X-ray tube has great influence on the X-ray fluorescence (XRF) analysis. During the correction of the absorption and enhancement effect, the fundamental parameter method requires the accurate primary spectrum of of X-ray tube. The X-ray spectrum after electron hitting target was calculated using the MCNP program, with different X-ray tube voltages, different target materials and different beryllium window thickness; The obtained spectroscopy data can reflect the spectrum characteristics under different conditions, and may be used for optimization of target material, high voltage and so on, to realize high accurate XRF analysis.