The invention provides an inorganic compound, and a preparation method and an application thereof. The inorganic compound has a chemical formula of Li7Te3O9F, belongs to a hexagonal crystal system andspace group P63, and has cell parameters as follows: a is equal to b which is in a range of 11.3 to 11.5 angstroms; c is in a range of 4.7 to 4.9 angstroms; alpha is equal to beta which is 90 degrees; gamma is 120 degrees; and Z is 2. The inorganic compound provided by the invention is prepared through a high-temperature solid phase method, is an ultraviolet-visible nonlinear optical crystal containing a lone pair electron group and a tetrahedron element, shows strong frequency-doubled effect, wide light transmittance range and high thermal stability, and can be used as a nonlinear optical crystal material and applied to the field of laser frequency conversion.