In order to monitor the freshness of banana in the process of storage and transportation, an electronic tag type banana releasing gas sensor which includes tag antenna and gas sensitive film is designed. At resonance frequency of 915 MHz, a bowtie tag antenna is designed with electromagnetic simulation software. The multiwalled carbon nanotube is selected as the gas sensitive material by comparing the complex impedance of five kinds films. With the incorporation of a small amount of conductive carbon paste, the impedance regulation of the gassensitive film is successfully resolved, and the impedance matching between the antenna and the gas sensor is achieved. The gas sensitive testing platform is established to test the response characteristic of the sensor for banana releasing gas at different maturity. The experimental results indicate that the tag gas sensor has a good response and recovery characteristic for banana releasing gas. The resonant frequency change of sensor is 9, 36, 18 MHz when banana is in fresh, ripe, and rotten period respectively. Therefore, the freshness of banana can be qualitatively identified.