Stable structures of nitrogen-rich sulfides SN4, N3SN4, and S(N4)m2− (m=1–4) were studied. Two of SN4, three of SN42+, two of SN42−, one of SN4− and two transition structures of the dissociation reactions of SN4 were obtained. Four stable species of N3SN4, and a transition structure of the dissociation reaction of N3SN4 were calculated. In the set of S(N4)m2− (m=2–4), the sulfur atom with large atomic radius and loose electron density allows it connect more nitrogen clusters N4 to form nitrogen-rich sulfides S(N4)m2−. SNx may be used as high energy-density material combining with opposite ion.