Exponential rise in wireless data demands is already creating a significant burden on current mobile networks. Meanwhile, the upcoming 5G system is believed to consist of heterogeneous access networks. The user satisfaction and radio resource efficiency are the main challenges for the network convergence. Network virtualization technology is regarded as an effective solution to above challenges. Heterogeneous networks are virtualized to multiple logical slices to best serve specific services. Two fundamental questions are how to virtualize mobile resources among different slices, and how to shield the impact of time-varying wireless channel on slicing with Quality of Service (QoS) guaranteed. In order to solve these two problems, we propose a two-timescale Virtualized Radio Resource Pre-Allocation mechanism, consisting of the inter-slice pre-allocation and the intra-slice scheduling. Specifically, the subcarrier and transmission power are jointly optimized and the base station coordination is also supported. For different network deployment scenarios, both the centralized and distributed solutions are provided. Simulation results demonstrate that both solutions are able to guarantee the QoS with the minimum requirements of radio resource.