In this thesis we present pvFPGA, the first system design solution for virtualizing an FPGA - based hardware accelerator on the x86 platform. The accelerator design on the FPGA can be used for accelerating various applications, regardless of the application computation latencies. Our design adopts the Xen virtual machine monitor (VMM) to build a paravirtualized environment, and a Xilinx Virtex - 6 as an FPGA accelerator. The accelerator communicates with the x86 server via PCI Express (PCIe). In comparison to the current GPU virtualization solutions, which primarily intercept and redirect API calls to the hosted or privileged domain’s user space, pvFPGA virtualizes an FPGA accelerator directly at the lower device driver layer. This gives rise to higher efficiency and lower overhead. In pvFPGA, each unprivileged domain allocates a shared data pool for both user - kernel and inter-domain data transfer. In addition, we propose the coprovisor, a new component that enables multiple domains to simultaneously access an FPGA accelerator. The experimental results have shown that 1) pvFPGA achieves close-to-zero overhead compared to accessing the FPGA accelerator without the VMM layer, 2) the FPGA accelerator is successfully shared by multiple domains, 3) distributing different maximum data transfer bandwidths to different domains can be achieved by regulating the size of the shared data pool at the split driver loading time, 4) request turnaround time is improved through DMA (Direct Memory Access) context switches implemented by the coprovisor.