Analyses were made on the security threats and weakness of present group signature schemes, and a dynamic group signature with forward security based on elliptic curves cryptosystem was presented. The identity blinding process and probabilistic encryption algorithm of the scheme enable the signature group to be dynamic without changing the group public key and private keys of all the group members. The scheme avoids the direct relationship between signature complexity and group scale, prevents coalition attack and generalized signature forgery. If a signature is successfully attacked or the anonymity tracing protocol is executed, other group signatures generated by the same member earlier and signatures generated by other members are still secure and anonymous, so the group signature scheme proves to be forward secure. Further detailed analyses also justify its brevity, security, high efficiency, and thus considerable improvement on system overheads regarding software and hardware application.