In the cloud computing, the statistical multiplexing is a remarkable character, and the utilization efficiency of physical resource can be improved through the virtual technology. Aiming at the load balancing problem of the resource utilization needed to be discussed in the cloud virtual machine cluster, a Software Defined Network (SDN) based Anti-Saturated Grouping Strategy (ASGS) method was proposed according to the OpenStack cloud platform. The cloud hosts were separated into different groups based on their weights, and then the load information of cloud hosts were obtained by the SDN controller which used the probe with different groups periodically. When a request came, a group was selected randomly using the average weight of each group cloud hosts by the load balancer, and a proper backend was chosen by the polling method within the group. In order to avoid the cloud host downtime caused by the sudden increased requests for too many resources of a backend, the cloud host with higher weight was given a default parameter to increase the weight, and then the host would receive fewer requests on the higher load status. The experimental results show that, whatever the request number changes, the resource utilization standard variance of the proposed ASGS is always smaller than the random and round robin methods when time varies, which is nearly 0. The proposed ASGS has better load balance for the cloud host cluster.