Now many television operators are providing subscribers with more and more value-added service. When people use these services they will have the risk of leaking personal information, such as the watching habit, the privacy problem has become a hot topic to the public. This paper proposes a scheme of CAS anonymous authentication in two-way network, and the scheme uses group signatures based on the elliptic curve. It meets both efficient authentication and transaction tracking needs, and can also protect user's privacy in a certain extent.