In order to solve the problem that the BER and spectral efficiency restrict each other in the traditional modulation methods, we design a novel signal modulation and demodulation method where the cosine signal and the chirp signal are used as carriers to transmit cooperatively. In the modulation, each signal of the traditional QPSK modulation is inserted by a chirp signal to form the mix modulation. In this case, the new modulation will permit the four signals to transmit simultaneously; In the demodulation, consisting of the carrier signals, we design eight integrators. Moreover, the signals will be estimated by the maximum value of integral results. Numerical results imply that this modulation and demodulation method improves both BER and the bit pass rate.It means that the modulation and demodulation method we design in this paper obtains the comprehensive advantages between BER and spectral efficiency, and enhances the effective capacity of the system.