A system for measuring a permittivity includes a resonant chamber, a conductive probe, a platform, a pillar, a detector, and a computing module. The resonant chamber has a cavity. The conductive probe is configured for introducing a microwave into the cavity of the resonant chamber. The platform is configured for carrying a sample. The pillar is positioned between the platform and a chamber wall, so that the platform protrudes from the chamber wall. The detector is used to detect a resonant frequency of the microwave when resonance occurs within the cavity. The computing module is configured for calculating a permittivity corresponding to the measured resonant frequency according to a corresponding relationship between resonant frequency and permittivity. The above-mentioned system for measuring a permittivity is capable of measuring a broader range of permittivity with simplified measurement steps and higher accuracy. A method for measuring a permittivity is also disclosed.