At present, the communication of the Internet of vehicles relies on the LTE or 5G wireless communicationchannel of the cellular network. To address the most common security threats in the communication of Vehicular Ad-Hoc Network in the 5G Era, this paper proposes a dynamic group authentication and key agreement protocol based onC-V2X (vehicle to everything based on the cellular network), which is called V2X-GKA for short here. The scheme isbased on the difficulty of ECDLP (Elliptic curve discrete logarithmic problem), which makes it impossible for an attackerto forge a certificate to pass security authentication; based on the difficulty of DBDH (Decisional Bilinear Diffie-HellmanProblem), secure key agreement in the group is realized, so that the attacker cannot obtain the shared key. It guarantees thesecurity of the key and solves the problem of key escrow. This scheme combines authentication and group key agreement torealize the dynamic group member management. The session key can be updated safely and dynamically without executingall the protocols when a group member is revoked or a new member is added. It not only assures the group’s forwardand backward security, but also reduces the algorithm’s complexity, making it suitable for a real-time high-speed mobileapplication environment. Through security analysis, it is proved that the V2X-GKA scheme in this paper meets the existingsecurity objectives, and because the protocol is configured on the open channel, it has a certain completeness and superioritycompared with similar schemes.