The expression is given for the spectral distribution of X-ray tubes with grounded cathode. The expression takes into account the excitation of X-ray radiation of the first and second generations backscattered electrons. The bremsstrahlung and characteristic spectral components are calculated for chromium, rhodium and tungsten anodes for different voltages at the X-ray tube anode. It is shown that the intensity of the long-wavelength component of the X-ray tubes with grounded cathode bremsstrahlung spectrum in some cases can exceed twice the intensity of this part of the spectrum for tubes with grounded anode. The intensity of the long-wavelength lines of the characteristic spectrum is also enhanced substantially, but their peak to background contrast is somewhat less than the contrast of these lines for the case of a high potential at the X-ray tube cathode.