Software defined network (SDN), which introduces centralized controllers to drastically increase network programmability, has been a hot topic in the network domain. Software defined network separates control plane from data plane of network equipment, establishing a good platform for network virtualization. As the network scales up, the performance of SDN virtualization framework becomes a key bottleneck. Still, current SDN virtualization frameworks lack support for fine-grained parallelism, making them challenging for developers to fully exploit many cores to virtualize large networks. This paper presents a novel API and runtime for fine-grained parallel programming in SDN virtualization framework. By abstracting flows and network resources, the framework programming model enables developers to easily write programs to directly define various virtual networks and parallelly operate the network resource or flow objects by a lock-free manner. Experimental results show that the presented framework has a better logical control performance, allowing one to implement rich functional virtual networks.