Abstract: Based on the features of the cyclic-spectrum density of CPM-signal, we first propose an in-depth study on the internal relationship of the Modulation Order and the cyclic-spectrum density of M-order CPM-signal. Then we develop a novel blind identification algorithm of Modulation Order based on cyclostationarity, which provides the theoretical foundation and the feasibility of the blind demodulation of CPM-signal. The proposed algorithm can be suitable for CPM-signal with any arbitrary modulation index and Frequency-Shaping Pulse. The simulation study shows that the algorithm has the power to provide a good identification of Modulation Order. In addition, the algorithm is less affected by Gaussian noise and easy implementation