The invention discloses a silicon nitride membrane strained GeSn infrared LED device and a preparation method thereof. The infrared LED device comprises an Si substrate and a Ge buffer layer arranged on the silicon substrate, wherein the Ge buffer layer is successively provided with an aluminum electrode, a transverse P-I-N GeSn layer, a silicon nitride layer and an aluminum electrode from the left to the right, and a silicon nitride film is deposited above a GeSn P-I-N structure. According to the invention, the device and the method are compatible with a CMOS process, the problem of difficulty in growing a GeSn alloy with a high stannum ingredient content in the prior art is overcome, the stress size can be changed through adjusting the structure of a silicon nitride membrane so as to realize the demand of a GeSn material light source for different-wavelength light, the photoelectric conversion efficiency is quite high, the light stability is high, the processing is simple and convenient, and a concrete structure and a concrete implementation scheme are provided for realization of a light source on chip.