Scalability is an important metric which is used to evaluate the scalability of the cluster system. Although, there have been a lot of scalability metrics, the research of scalability of the cluster system is very few. Common scalability evaluation methods are usually used to analyze the scalability of the algorithm. They can also be used to analyze the scalability of the cluster. These methods are not only theoretically feasible, but not suitable for specific testing. In order to eliminate this defect, a simple and efficient testing method is proposed. This method, in the paper, is mainly used for the actual test. Using the method given in the paper, we can measure the scalability performance of the cluster system easily and effectively.