The crystal of tetrahydrothiazole—2-thione(TTT)belongs to monoclinic system.Spacegroup P2_1/n.There are eight molecules in an unit cell with parameters a=13.844(7),b=5.614(2),c=13.516(7),β=95.08(5)°,V=1046.3 (9).~3 The three dimensional intensity datawere obtained on a Syntex R3 four-circle diffractometer,and the number of the independent diffrac-tions amounted to 1906.The structure was solved by direct method and refined by block-diagonal least-squares method.The final R is 0.082.In crystal,the molecular structure is between 1 and 2 in which S(1),S(2),Nand C(1)are coplanar with conjugation.We use CNDO/2 programmes written by ourselves on Eclipse computer to compute the electronicenergies,molecular total energies,dipole moments,the charge densities and net charges of each atomof TTT and its N-benzoylated derivative.The color of the acylated TTT and its properties for aminolysis are discussed. The crystal of tetrahydrothiazole-2-thione (TTT) belongs to monoclinic system. Space group P2_1 / n.There are eight molecules in an unit cell with parameters a = 13.844 (7), b = 5.614 (2), c = 13.516 ), β = 95.08 (5) °, V = 1046.3 (9). ~ 3 The three dimensional intensity datawe obtained on a Syntex R3 four-circle diffractometer, and the number of the independent diffrac tions amounted to 1906.The structure was solved by direct method and refined by block-diagonal least-squares method. The final R is 0.082. In crystal, the molecular structure is between 1 and 2 in which S (1), S (2), Nand C coplanar with conjugation. We use CNDO / 2 programs written by ourselves on Eclipse computer to compute the electronicegies, molecular total energies, dipole moments, the charge densities and net charges of each atom of TTT and its N-benzoylated derivative. the color of the acylated TTT and its properties for aminolysis are discussed.