This paper reports that the splitting of potential energy curves for the low-lying or low excited states for hydride molecules (cations) (MgH, A1H+, SiH, PH+, SH,CIH+) of the third period under Spin-Orbit Coupling has been cal- culated by using the Spin-Orbit Multi-Configuration Quasi-Degenerate Perturbation Theory (SO-MCQDPT) method. Then, spectroscopic constants of the split states have been derived from the Murrell-Sorbie function. The calculated dissociation energies for the spectrum branch terms have been given, respectively. The spectroscopic constants and dissociation energies for the spectrum branch terms are given for the first time in this paper.