The objective of the present disclosure is to provide a method, apparatus and system of ACK/NACK reporting for Cat-M mechanism. Here, a user equipment feeds back an ACK/NACK message to an eNB on PUSCH based on received downlink data, wherein when computing the number of resource elements occupied by the ACK/NACK message on PUSCH, the number of OFDM symbols in a guard period is ruled out. This may effectively lower the UE's PUSCH data code rate, and meanwhile enhance the eNB's decoding performance on PUSCH.