Abstract: To keep fresh and quality of postharvest fruit & vegetable, it is the most important to provide storage environments with high relative humidity (RH). Currently in China, the two mainly used humidification methods are packaging with plastic membrane/bag and installing ultrasonic humidifier in the storage room. All these methods have different degree of disadvantages. In order to provide steady high RH and keep fresh for unpackaged fruits & vegetable under storage, a kind of dry-fog controlled humidifier system was designed and built. Main parts of the system are humidity sensor, Israeli made atomizer with orifice size of 5 mm, water purification system, air compress system, purified water storage tank, pressure regulation and controlling device, water and air transportation tubes, and micro-computer controlling terminal. Mists generated through the fogger had average particle diameters of 2-10 μm, which can rapidly spread and integrate into surrounding environment air, providing RH as high as 90%-98%. The humidity sensor in the storage room can continually sense changes of humidity and transmit the signal to the micro-computer controlling terminal, then the controlling unit can automatically control on or off of the atomizer. So that RH in the storage room can keep at the setting point level, and this was demonstrated by RH monitor within 24 hours after system and responding efficiency tests. Application test and evaluation on fruit & vegetable fresh keeping was conducted, and the results showed that tested fruit & vegetable stored under dry-fog controlled humidifier had much less weight loss than those stored under natural RH condition, but at the same water content level as those packaged with plastic bag. In addition, storage time and shelf life of the tested fruit and vegetable exposed to the dry fog was doubled as compared to those stored in the natural RH condition. Overall sensory quality index of dry-fog exposed fruit and vegetable was also improved. Moreover, attributes of controlling decay incidence and delaying decay development were also found with dry-fog controlled humidity system during postharvest storage period (data not shown). Finally, evaluation and analysis of installation and usage cost of dry-fog controlled humidity system was done. In conclusion, advantages of dry-fog controlled humidity system are no water condensation under low temperature, keeping the cooling storage room ‘dry’ with high humidity, saving energy and labor work, and protecting environment. These findings suggest that the application of dry-fog controlled humidity system has major benefits on postharvest storage of fresh fruit and vegetables.