Grid services allow the services to be seen as a seamless information processing system that the user can access from any location, the Grid resources are often distributed, autonomic, heterogeneous and dynamic, and they are accessible through the Internet, when users and cooperant servers communicate with a server. Distributed Denial-of-service can make the service requests become hard to implement. An intrusion tolerant mechanism against the attack is formalized for Grid services based on the mechanism design analysis of game theory in this paper. The problems that the attackers could use the authentic IP addresses of the zombies to hide the source of attacks and to increase the computational ability and the likelihood to filter out legitimate traffic are effectively settled under the mechanism. The condition for the legitimate clients being served successfully is further deduced to give an instruction for clients.