As a constant envelope modulation method, continuous phase modulation has high bandwidth and power utilization, and strong anti-interference ability, which is very suitable for the physical layer waveform design of Satellite-Terrestrial Integrated Network in 6G full coverage scenarios with nonlinear power and limited bandwidth. However, the complexity and real-time requirements of CPM demodulation algorithms are high, and most of the research focuses on algorithm performance evaluation and simulation, and lacks engineering application implementation. Therefore, based on the real-time high-speed data processing capability of Digital Signal Processing (DSP), a practical CPM modulation and demodulation system is designed, in which the data at the sender is first obtained coding gain by Trellis Coded Modulation (TCM), and then CPM modulation is carried out to form a constant envelope modulation signal, and the Viterbi algorithm (VA) is used at the receiver. The demodulation of CPM signals is realized. The effectiveness of the proposed system has been verified through simulation evaluation and practical testing in high-speed narrowband frequency hopping data transmission radios, indicating that the system has good stability and practicality, providing support for the application of CPM in 6G Satellite-Terrestrial Integrated.