The volatile nature of Cloud user’s needs is considered a worthy challenge in formulating the Service Level Agreement (SLA) negotiation. The sterility of the standard SLA templates in handling the diversity in the users’ requirements motives the concept of the dynamic SLA. Establishing the SLA contract is mainly based on converting the user’s QoS requirements into a meaningful Service Level Objectives (SLO) during the negotiation phase, but in case of modification in these QoS requirements especially during the run time, the current negotiation may be violated and the provider may resort to terminate the current negotiation and re-establish it. This paper presents a novel methodology based on arithmetic and fuzzy logic model to establish a dynamic SLA’s Negotiation system commensurate with the dynamic aspects of the Cloud environment. The proposed negotiation system mainly based on defining pre conditions and decisions to modify only the required SLO at the run-time without completely hang-up the SLA.