Abstract: By adopting the idea of PKI/CA，a guarantee based cloud computing architecture is proposed in this paper to embolden cloud computing with a credit system，one of the major tasks in the marketing and socializing process of cloud computing nowadays.In this architecture，some special agents are introduced to offer paid guarantee for services in cloud computing，and to compensate invoking users when the services invoked fail.In addition，after a detailed analysis of the bankrupt risks of the guarantee agents，a simulation is conducted to demonstrate the effectiveness of this guarantee based approach.The simulation results show that the accumulative asset-loss for each user changes more gradually；the ability of risk-resistance of each user is strengthened；the total amount of service-invocations increases；and accordingly the total benefits of cloud computing can also be enlarged.