Large-scale graph processing is gaining increasing attentions in many domains. Meanwhile, FPGA provides a power-efficient and highly parallel platform for many applications, and has been applied to custom computing in many domains. In this paper, we describe FPGP (FPGA Graph Processing), a streamlined vertex-centric graph processing framework on FPGA, based on the interval-shard structure. FPGP is adaptable to different graph algorithms and users do not need to change the whole implementation on the FPGA. In our implementation, an on-chip parallel graph processor is proposed to both maximize the off-chip bandwidth of graph data and fully utilize the parallelism of graph processing. Meanwhile, we analyze the performance of FPGP and show the scalability of FPGP when the bandwidth of data path increases. FPGP is more power-efficient than single machine systems and scalable to larger graphs compared with other FPGA-based graph systems.