The integrated sensing and communication (ISAC) has been envisioned as a promising technology to simultaneously perform high-capacity communication and high-accuracy sensing with efficient resource utilization. Nevertheless, due to the severe mutual constraints between communication and sensing functions, the performance of previously reported ISAC demonstrations notably trails that of individual communication or sensing systems. In this work, an integrated LFM-QAM waveform is proposed and theoretically analyzed by combining linear frequency modulation (LFM) and quadrature amplitude modulation (QAM) formats. Employing the proposed waveform and optical wavelength division multiplexing (WDM) technique, we experimentally implement a multi-channel photonic terahertz (THz)-ISAC wireless system operating at 275 GHz band, simultaneously achieving a communication data rate up to 120 Gbps and a range resolution as high as 2.5 mm. To the best of our knowledge, this is the first time to demonstrate beyond 100 Gbps wireless data rate and mm-scale resolution based on an integrated waveform in the THz region, revealing the potential of THz-ISAC performance.