Recently, hybrid Satellite-Terrestrial (S-T) communication system, especially satellite communications integration with 5G/6G, is regarded as future development trend. Considering physical layer access waveform design, this paper proposed a novel Generalized Frequency Division Multiplexing- Code Division Multiple Access (GFDM-CDMA) scheme for hybrid S-T communication system. GFDM has many advantages such as good adaptability and low out-of-band (OOB) radiation. However, because of its interference between adjacent subcarriers, the multiple access performance is degraded. In this paper, we introduced (CDMA) technology in GFDM. The odd and even subcarriers of GFDM are spread spectrum respectively. Moreover, this scheme integrates the slot-ALOHA protocol and GFDM-CDMA, which extends access freedom in frequency, time and code domain. The simulation and analysis results show that the proposed GFDM-CDMA scheme is effective and suitable for hybrid S-T communication system.