A rather exhaustive theoretical study is performed on the doublet potential energy surface (PES) of the NC3S system at the B3LYP/6-311G(d), OCISD/6-311G(d), and single-point CCSD(T)/6-311G(2df) levels. A total of 40 minimum isomers are located including chainlike, cyclic, cagelike, and weakly bound species, which are connected by 81 interconversion transition states. At the CCSD(T)/6-311G(2df)//QCISD/6-311G(d)+ZPVE level, the lowest-lying isomer is a linear structure NCCCS 1 (0.0 kcal/mol). Its calculated vibrational frequencies and rotational constant are in good agreement with recent experimental values. Additionally, eight new isomers with high kinetic stability are predicted to be possible candidates for future experimental and astrophysical detection. They include five chainlike species, i.e., linear CNCCS 2 (26.9), bent CCNCS 3 (56.9), bent CCSCN 4 (62.7), bent CCSNC 5 (85.4), linear CCCNS 6 (67.0), and three three-membered ring species NC-cCCS 9 (34.2), 9' (40.9), and CN-cCCS 10 (57.1). Structural analysis show that these isomers can be considered as adducts formed by various S atom attacks (terminal atomic-addition, side Cequivalent toC addition and internal single-bond insertion) to the C3N radical (CCCN or CCNC). The present NC3S potential energy surface represents the first detailed study on the isomerization and dissociation mechanism of the NCnS series, and it is expected be useful and informative for further investigation of even larger NCnS species for which complete isomeric survey is very expensive.