The invention provides tofacitinib nanocrystal eye drops for treating immunity-related eye diseases and a preparation method thereof, and the tofacitinib nanocrystal eye drops are prepared by the following steps: dispersing micronized tofacitinib in a surfactant solution at a high speed, then mixing with a stabilizer, uniformly dispersing, and then carrying out high-pressure homogenization circulation, so as to obtain the tofacitinib nanocrystal eye drops. The tofacitinib nanocrystal eye drops meeting the particle size requirement are obtained. Wherein the surfactant is P188-lecithin, and the stabilizer is any one or a mixture of more of HPMC (Hydroxy Propyl Methyl Cellulose), polyvinyl alcohol and HPMC-docusate sodium. Through cooperation of the surfactant and the stabilizer, the particle size and the potential of the eye drops are influenced, the stability and the adhesiveness are improved, the residence time of the medicine in eyes is prolonged, and the medicine carrying rate is high. The loss speed of the medicine in front of the cornea is reduced, so that the medicine can be slowly released, the eye drop frequency of a patient is reduced, the compliance of the patient is improved, and a good clinical application prospect is achieved.