The integration of high-speed communication and high-precision sensing is key in 6-Generation (6G) networks. A signal generation and transmission scheme for optical terahertz communication based on phase shift keying (PSK) and linear frequency modulation (LFM) is proposed, where geometric shaping (GS) technology is utilized to improve the communication capacity of integrated signals. Theoretical analysis was conducted on the generation, transmission, sensing, and communication principles of the GS-PSK-LFM integrated signal, and the ambiguity function of the integrated signal was analyzed. Based on MATLAB and VPI simulation environments, the communication and sensing performances of 8PSK-LFM and GS-8PSK-LFM formats at rates of 4 and 8 Gbaud were analyzed, as well as the effects of different DC offsets on the communication and sensing performances. The results show that the maximum peak-to-side lobe ratio (PSLR) of the proposed integrated signal theory is 10.5 dB at a rate of 4 Gbaud, and the distance resolution reaches 0.97 cm. Under a wireless channel-transmission distance of 50 m, the communication transmission rate can reach up to 24 Gbit/s, and the error rate is lower than the hard decision threshold of $\mathrm{3.8}\times {\mathrm{10}}^{-\mathrm{3}}$. At the same bit error rate, when combined with GS, the input optical power of the sensing signal photoelectric detector (PD) is reduced by a maximum of 0.43 dB compared with that of 8PSK-LFM. When the DC offset is 1, the communication and sensing performances are balanced. Thus, this may be considered in future scenarios where sensing is prioritized.