In this paper, a composite hydrogel film (Au/Me-SiO2/G) based on Au nanoparticles, mesoporous silica and gelatin was prepared, which can be used for low relative humidity (RH) detection. Au-1%/Me-SiO2/G exhibits a response of 423% in the range of 0.4–30% RH, a short response time of 28 s, a linearity of R2 = 0.997, and good long-term stability. With the outstanding ability to adsorb water molecules, the sensor can detect NH3 at room temperature and low humidity environment. The response of the sensor to NH3 significantly increases with the humidity. At 30% RH, the initial impedance value of the sensor is as low as ∼6.6 MΩ, and the response to 50 ppm NH3 is 78%. In addition, an egg storage scenario was simulated, and the water loss in eggs was monitored simultaneously by the prepared humidity sensor and a commercial sensor. The results demonstrate the practical application detection ability of the prepared humidity sensor.

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