Digital terrestrial Television Multimedia Broadcasting-Advanced(DTMB-A), is a new type of illuminator of opportunity for passive radars, which has broad bandwidth and excellent adaptability against multipath effect. In this paper, DTMB-A signal Ambiguity Function(AF) is concluded and the mechanism of intra-frame and inter-frame ambiguity peaks is researched by theoretical derivation and simulation verification. The analysis shows that the period deterministic frame structure(the synchronization channel and guard interval) is the main factor that causes the ambiguity sub-peaks. Therefore, a DTMB-A signal ambiguity functions suppression method is proposed by using non-uniform sampling, which has low computational complexity and is convenient for parallel computing. Simulation results show that this method can suppress DTMB-A signal Ambiguity Functions into almost ideal thumbtack shape effectively, which is the foundation of detecting target on DTMB-A passive radar.