Abstract: This paper introduces application of waterproof ventilated valve in sealed box of radar．Phenomenons that the waterproof ventilated valve is able to balance the air pressure in and out of the sealed box，avoid sealing failure caused by structural changes and eliminate cavity seeping caused by“breathing effect”are discussed．The attributes of the air inside the sealed box are calculated，the mechanical deformation of cavity configuration is analyzed by simulation，thus providing the theoretical foundation for the selection of waterproof ventilated valve．Experimental validation and random test indicate that waterproof ventilated valve can improve the operation environment of components inside sealed box and raise the reliability and service life of subassemblies．