The communication and ranging composite system can realise information transmission and distance measurement at the same time, which reduces the complexity of the system and expands the application scope. In order to improve the communication rate and the time delay estimation accuracy in low Signal-to-Noise Ratio (SNR) of the composite system, the Parallel Combinatory Spread Spectrum (PCSS) technology is applied, and the mW composite sequence is used as the spread spectrum sequence, and the improved generalised crosscorrelation algorithm is adopted. The algorithm performs exponential calculation on the correlation function, then the correlation function obtained by inverse Fourier transform is performed as a high power operation, and finally performs the time delay estimation. The simulation results show that the improved communication and ranging composite system improves the information transmission rate and has better time delay estimation performance. The proposed system can accomplish ranging and communication tasks more effectively.