Rain erosion is a critical problem in the use of conventional Zinc Sulfides as infrared window and dome. In this study, the diamond-ZnS composite, which dispersed diamond particles into a zinc sulfide matrix, was fabricated for improved durability against rain erosion. It was found that mechanical properties, such as hardness, fracture strength and Young modulus of the diamond-ZnS composite improved with the increase in diamond particles. Furthermore the diamonds-ZnS composite consisted of two layers, a diamond dispersed layer and a pure ZnS layer. They have a 280-350kg/mm2 hardness, which is 1.5 times higher than conventional ZnS, while maintaining about 55~70% in average transmittance at the wavelength of 10micrometers bands.