In this paper, the scaling laws between the X-ray temperature and the X-ray energy converted by laser have been studied analytically for the laser cylindrical cavity targets according to the information of the experiments and the numerical simulations. For a series of experiments made on the Shenguang facility in 1989, we predict that, as the laser energy of each beam is 300-500J, the pulse width is 0.7-1.0ns, and the wavelength is 1.06 μm, the X-ray conversion efficiency is about 50-55% for the two beam targets, and the corresponding X-ray temperature is about 1.5×106-1.7×106K.