There is recent interest in atomic inner-shell two-photon decay processes because state-of-art experimental techniques (such as electronic coincident measurement etc.) have made it possible to measure the two-photon decay rate in the X-ray region. We perform relativistic self-consistent field calculations on the two-photon decay rates of (ls)-1→(ns)-1 transitions (n = 2,3,4) and (ls)-1→(nd)-1 transitions (n = 3,4) for hydrogen, hydrogen-like Xe ion and Xe atoms. Comparing the hydrogemc and the hydrogen-like Xe ion rates, we can clearly demonstrate the relativistic effect. Comparing our previous non-relativistic and our present relativistic Xe atom rates, we can also demonstrate the relativistic effect in the atomic inner-shell two photon decays. Comparing the hydrogen-like Xe ion and the Xe atom rates, we can explain the atomic screening effect. After elucidating the relativistic effect and the atomic screening effect, we are convinced that we have obtained the reliable relativistic rates, which can provide a basis to analyze th effect of electron correlations in the atomic inner-shell two-photon decays. We also compare our results with the experimental measurement and other theoretical results.