The reaction mechanisms of HNCS with NH(X3∑) were theoretically investigated. The minimum energy paths (MEP) of the reaction were calculated by using the density functional theory(DFT) at the B3LYP/6-311 + + G** level. The equilibrium structural parameters, the harmonic vibrational frequencies, the total energies, and the zeropoint energies(ZPE) of all the species were calculated. The single-point energies along the MEP were further refined at the QCISD(T)/6-311 + + G** level. It was found that the mechanisms of the HNCS + NH(X3∑) reaction involve two channels producing the HNC + HNS and the N2H2 + CS products. Channel 1 plays a dominant role and the HNC + HNS are the main products. The reaction is exothermic.