An MIC verification method in D2D communications and a D2D communications system include: a monitoring UE receives a discovery announcement message from an announcing UE, in which the discovery announcement message carries a 32-bit MIC, and the MIC is a signature value obtained when the announcing UE conducts, by using a private key, a digital signature on a current time and a time window in the discovery announcement message; and the monitoring UE verifies the correctness of the MIC by using a public key of the announcing UE to determine whether the discovery process is successful.