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Nonlinear optical (NLO) crystal is the key component in all-solid-state lasers. Herein, a new tungsten oxyfluoride with O/F orientationally order, K 2 (H 2 O)WO 3 F 2 , has been successfully obtained. It is interesting that the distorted [WO 4 F 2 ] octahedra are induced by the trigonal [K 2 (H 2 O)]2+ motifs into an oriented arrangement. Remarkably, K 2 (H 2 O)WO 3 F 2 exhibits the strongest phase-matching second-harmonic generation (SHG) response of 6 × KH 2 PO 4 and the highest laser damage threshold of 274.45 MW/cm2 among reported transition-metal oxyfluorides. Theoretical calculations eluciate that its large SHG response mainly derives from the uniform alignment of the distorted [WO 4 F 2 ] octahedra. This result is beneficial to the modulation of anion order and the exploration of high-performance NLO materials. [Display omitted] • K 2 (H 2 O)WO 3 F 2 exhibits the strongest phase-matching SHG response of 6 × KDP and the highest LDT of 274.45 MW/cm2 among reported TM oxyfluorides. • K 2 (H 2 O)WO 3 F 2 possesses a wide transparency window of 0.35–2.5 µm and a suitable birefringence of 0.147 @ 1064 nm. • This research firstly reveals the effect of the trigonal [K 2 (H 2 O)]2+ motif on the formation of NCS structure. [ABSTRACT FROM AUTHOR]