Cloud computing is an environment which provides services for user demand such as software, platform, infrastructure. Applications which are deployed on cloud computing have become more varied and complex to adapt to increase end-user quantity and fluctuating workload. One popular characteristic of cloud computing is the heterogeneity of network, hosts and virtual machines (VM). There were many studies on cloud computing modeling based on queuing theory, but most studies have focused on homogeneity characteristic. In this study, we propose a cloud computing model based on open Jackson network for multi-tier application systems which are deployed on heterogeneous VMs of IaaS cloud computing. The important metrics are analyzed in our experiments such as mean waiting time; mean request quantity, the throughput of the system. Besides that, metrics in model is used to modify number VMs allocated for applications. Result of experiments shows that open queue network provides high efficiency.