Managing computation resources in a cost-effective way has become the core competence for a Cloud provider to win over the market because of the "pay-as-you-go" business model. Therefore, VM placement has become more and more important in the research and practices of VM management by determining at what condition and on which physical server a VM should be placed so that the SLA can be guaranteed and servers' utilization can be improved. Much existing work simply formulates the above issue to be a bin-packing problem, which does not take the VM relationships into account. However, the relationship information can greatly impact the SLA of the Cloud system and the resource utilization. Therefore, in this paper, we propose a relationship-based VM placement framework, SmartCRS, to optimize the VM placement procedure. SmartCRS reveals the relationships between VMs automatically. Then by using such information and based on a constraint library, it gives a proper VM placement plan. Finally, the plan is carried out by SmartCRS automatically or by Cloud administrators manually to improve the server utilization and guarantee the required SLA. Two case studies are conducted to demonstrate the effectiveness and efficiency of the proposed framework at the end of this paper.