We present a comprehensive study on

We present a comprehensive study on the X-ray evolution of late-type galaxies over the 14 Gyr of cosmic history, with evolutionary population synthesis. Our calculations reveal a decrease of the X-ray luminosity-to-mass ratio Lx/M with time, in agreement with observations. We show that this decrease is a natural consequence of stellar and binary evolution and mass accumulating process in galaxies, which may not be used as the indicator of intense star formation processes for lower-mass galaxies as suggested before. The X-ray-to-optical luminosity ratio Lx/LB is found to be fairly constant, and insensitive to the star formation history in the galaxies.