Rocking curves of reflection high-energy electron diffraction (RHEED) were observed from Si(111)-(7 X 7) surface at temperature of 293, 523, and 653 K by a RHEED apparatus with a magnetic deflector to change the glancing angle. The temperature dependence of RHEED intensity was calculated with change of the real and imaginary part of the potential corresponding to the thermal diffuse scattering arising from a thermal vibration of atoms, which was obtained by the way proposed by Dudarev et al. [Surf. Sci. 330, 86 (1995)]. We assumed that the amplitude of the thermal vibration (Debye parameter) increases with temperature according to the Einstein model. By comparing with the experimental results, the atomic positions of the (7 X 7) structure satisfying the observed RHEED rocking curves in this temperature range is determined. The positions of the surface atoms are almost coincident with the results obtained by using ab initio molecular-dynamics scheme (Brommer et al. [Phys. Rev. Lett. 68, 1355 (1992)]) within the difference of 0.01 nm.