Abstract: In order to improve the spectrum structure of random-polar modulated Extended Binary Phase Shift Keying with Continuous Phase (CP-EBPSK), a random-polar and M-ary modified CP-EBPSK (MCP-EBPSK) modulation with the adjustable coefficient of spectrum shape is proposed. The principle of random-polar and M-ary MCP-EBPSK is demonstrated, and the demodulator model based on muti-discrimination of digital impacting filter is also presented. The contrast and analysis of the power spectrum, the -60 dB bandwidth, the spectral efficiency, and the demodulation performance among the random-polar modulated CP-EBPSK, the random-polar modulated M-ary CP-EBPSK, and the proposed modulation, are carried out. Simulation results show that the proposed method not only multiplies the spectral efficiency, but also can get better demodulation performance by selecting the appropriate adjustment coefficient of spectrum shape.