The present invention relates to a sand protection device of rail vehicle air conditioning unit, comprising a sand protection filter screen disposed at a fresh air mouth, a secondary filter screen disposed in an evaporation cavity, a condensing cavity filter screen disposed in a condensing cavity, and a sand discharging baffle, wherein the back part of the sand protection filter screen is provided with an opening/closing door capable of opening or closing the fresh air mouth fast according to density of external inhalable particulate matters. After being pressurized by an automation pressure machine water generates water spray in the secondary filter screen via a pipeline and a plurality of evaporation cavity atomization nozzles connected to the pipeline; after being pressurized by the atomization pressure machine, water generates a high-pressure water column and water spray in the condensing cavity via a pipeline and a plurality of condensing cavity atomization nozzles connected to the pipeline. The lower part of a condenser is provided with the sand discharging baffle with a middle part higher than two side parts. The device of the present invention can ensure fresh air in carriages, improve the comfort level of passengers, prevent a lot of dusts from entering the carriage, and reduce the adverse effects to the heat transfer performance of the condenser caused by sands and dusts.