Abstract: According to the signal structure of China Mobile Multimedia Broadcasting (CMMB), this paper analyzes the ambiguity function of CMMB signal as illuminator of opportunity for passive radar systems. The mechanism of these ambiguity peaks is researched and compared with Europe Digital Video Broadcasting-Terrestrial (DVB-T) signal. As for the adverse effects because of the side peaks caused by cyclic prefix and Doppler ambiguity strips due to sync-signal, a method for suppressing these ambiguities is proposed. Simulation and experimental results show that the analysis of side peaks' mechanism is correct and the method can suppress side peaks effectively, which lays the foundation for target detection.