A photonic-aid tri-band multi-frequency measurement system based on a zero-IF architecture is proposed. An linearly frequency modulated (LFM) waveform and the signal under test (SUT) are carrier-suppressed double sideband modulated onto a dual-wavelength light wave. By utilizing a fiber Bragg grating (FBG) to perform optical spectrum separation, two frequency measurement channels are constructed. After post-processing of the measured waveform, a tri-band frequency-to-time mapping (FTTM) is realized. In the proof-of-concept experiment, single and multi-tone frequency measurement spanning 2-3.2 GHz, 6.7-7.9 GHz, and 11.9-13.1 GHz are demonstrated. Measurement errors below 3 MHz, 30 MHz, and 30 MHz, and a resolution under 0.8 MHz are achieved. Thanks to the zero-IF architecture and tri-band FTTM, the proposed scheme shows better robustness to image interference and measurement resolution compared with previous schemes based on high IF structures and single FTTM.