The present invention provides an optical ZnS material and a preparation method thereof, wherein the preparation method comprises: charging zinc and sulfur into a first crucible and a feeding device of a chemical vapor deposition furnace, respectively; heating the first crucible, the second crucible and a deposition chamber, and charging sulfur into the second crucible through the feeding device; introducing an inert carrier gas into the first crucible, and introducing an inert carrier gas and hydrogen into the second crucible, flowing the carrier gas containing zinc vapor and sulfur vapor respectively into the deposition chamber through pipelines to deposit ZnS, and supplying the second crucible with sulfur regularly and quantitatively through the feeding device during the deposition process to maintain a saturated vapor pressure of sulfur in a range of 0.8 to 1.8 KPa. The preparation method of the present invention does not generate H2S; thus it can avoid the formation of hydrogen-zinc complexes by H ions produced from the decomposition of H2S and Zn vapor, which would otherwise affect the transmittance and emissivity of ZnS material.