Abstract: The noise in HFC upstream channel is both complex and hard to predict, which has limited the networks’ development and application. According to the characteristics of uplink transmission and aiming at the defects of modulation selection constrained by the strong noise, the relationship between the uplink noise and modulation techniques was derived, which took the M-ray Pulse Position Shift Keying to improve the HFC uplink modem. The transmission characteristics of the MPPSK signals was deduced based on analysis of the electrical characteristics of the coaxial cable network. Using Matlab to model the transmission scheme, the MPPSK signals transmission in coaxial cable was simulated. The theoretical analysis and experimental results effectively showed that the SNR threshold was reduced and the spectrum efficiency enhanced, the BER was declined by 2-3 orders of magnitude, and 3-4dB saved in signal energy. The MPPSK modem demonstrates a better anti-noise performance than the traditional techniques.