The novel title compound 4-chlorobenzaldehyde (2-trifluoromethyl-5,6,7,8- tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidin-4-yl)hydrazone monohydrate (C18H14ClF3N4SH2O, Mr = 428.86) has been synthesized by a condensation reaction of 4-chlorobenzaldehyde with (2-trifluoromethyl-5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidin-4-yl)hydrazine, and its crystal structure was determined by single-crystal X-ray diffraction. The crystal belongs to monoclinic, space group P21/c with a = 7.4252(7), b = 26.344(2), c = 10.3095(9) , = 109.407(2)°, V = 1902.0(3) 3 , Z = 4, Dc = 1.498 g/cm3 , μ = 0.356 mm-1 , F(000) = 880, the final R = 0.0564 and wR = 0.1681 for 2343 observed reflections with I > 2 (I). X-ray diffraction analysis reveals that the title hydrazone molecule is nearly planar except for the cyclohexene and trifluoromethyl moieties. In the crystal packing, the molecules form stacks by a three-dimensional framework, which results from intermolecular N(3)-H(3)···O(1), O(1)-H(1B)···N(2), O(1)- H(1B)···N(4) and O(1)-H(1A)···F(1) hydrogen bonds via water molecules together with π-π stacking interactions. Molecular geometry of the title compound in the ground state optimized by B3LYP functional with 6-311G** basis sets indicates that the calculations are in agreement with the experimental data. The preliminary bioassay suggested that the title compound exhibits relatively good fungicidal activity against Fusarium oxysporium f.sp.vasinfectum and Dothiorella gregaria. The novel title compound 4-chlorobenzaldehyde (2-trifluoromethyl-5,6,7,8-tetrahydrobenzo [4,5] thieno [2,3- d] pyrimidin-4-yl) hydrazone monohydrate (C18H14ClF3N4SH2O, Mr = 428.86) has was synthesized by a condensation reaction of 4-chlorobenzaldehyde with (2-trifluoromethyl-5,6,7,8-tetrahydrobenzo [4,5] thieno [2,3- d] pyrimidin-4-yl) was determined by single-crystal X-ray diffraction. The crystal belongs to monoclinic space group P21 / c with a = 7.4252 (7), b = 26.344 (2), c = 10.3095 (9) ° V = 1902.0 (3)  3, Z = 4, Dc = 1.498 g / cm3, μ = 0.356 mm -1, F (000) = 880, the final R = 0.0564 and wR = 0.1681 for 2343 observed reflections with I> 2 (I). X-ray diffraction analysis reveals that the title hydrazone molecule is nearly planar except for the cyclohexene and trifluoromethyl moieties. In the crystal packing, the molecules form stacks by a three-dimensional framework, which results from intermolecular N (3) -H (3) ··· O (1), O (1) -H (1B) ··· N (4) and O (1) -H (1A) ··· F (1) hydrogen bonds via water molecules with π-π stacking interactions . Molecular geometry of the title compound in the ground state optimized by B3LYP functional with 6-311G ** basis sets indicates that the calculations are in agreement with the experimental data. The preliminary bioassay suggested that the title compound exhibits relatively good fungicidal activity against Fusarium oxysporium f.sp. vasinfectum and Dothiorella gregaria.